Late Roman army

The Late Roman army is the term used to denote the military forces of the Roman Empire from the accession of emperor Diocletian in 284 until the empire's definitive division into Eastern and Western halves in 395. A few decades afterwards, the Western army disintegrated as the Western empire collapsed. The East Roman army, on the other hand, continued intact and essentially unchanged until its reorganization by themes and transformation into the Byzantine army in the 7th century.

The army of the Principate underwent a significant transformation as a result of the chaotic 3rd century. Unlike the Principate army, the army of the 4th century was heavily dependent on conscription and its soldiers were more poorly remunerated than in the 2nd century. Barbarians from outside the empire probably supplied a much larger proportion of the late army's recruits than in the army of the 1st/2nd centuries. There is no evidence, however, that barbarian recruitment damaged the army's effectiveness.

The army of the 4th century was probably no larger in numbers than that of the 2nd. The main change in structure was the establishment of large armies that accompanied the emperors (comitatus praesentales) and were generally based away from the frontiers. Their primary function was to deter usurpations. The legions were split up into smaller units of comparable size to the auxiliary regiments of the Principate. In parallel, legionary armour and equipment were abandoned in favour of auxiliary equipment. Infantry adopted the more protective equipment of the Principate cavalry.

There is little evidence to support the theory that the role of cavalry was enhanced in the 4th century army as compared with the army of the Principate. It appears cavalry was much the same proportion of overall army numbers as in the 2nd century. Not does it appear that the cavalry's tactical role or prestige was any greater in the late army. Indeed, the cavalry acquired a reputation for incompetence and cowardice for their role in three major battles in mid-4th century. In contrast, the infantry retained its traditional reputation for excellence.

The 3rd and 4th centuries saw the upgrading of many existing border forts to them more defensible, as well as the construction of new forts with much higher defensive specifications. The interpretation of this trend has fuelled an ongoing debate whether the army adopted a defence-in-depth strategy or continued the same posture of "forward defence" as in the early Principate. There is little evidence that the location of 4th-century forts differed significantly from the early Principate, which, together with continued cross-border operations by Roman forces, adds weight to the case for continued forward defence. Whatever the defense strategy, it was apparently less successful in preventing barbarian incursions than in the 1st and 2nd centuries. This may have been due to heavier barbarian pressure, or to the practice of keeping large armies of the best troops in the interior, depriving the border forces of sufficient support.

Sources

Much of our evidence for 4th century army unit deployments is contained in a single document, the Notitia Dignitatum, compiled ca. 395–420, a manual of all late Roman public offices, military and civil. The main deficiency with the Notitia is that it lacks any personnel figures so as to render estimates of army size impossible. Also it was compiled at the very end of the 4th century; it is thus difficult to reconstruct the position earlier. However, the Notitia remains the central source on the late Army's structure due to the dearth of other evidence.

The main literary sources for the 4th century army are the Res Gestae (History) of Ammianus Marcellinus, whose surviving books cover the period 353 to 378. Marcellinus, himself a veteran soldier, is regarded by scholars as a reliable and valuable source. But he largely fails to remedy the deficiencies of the Notitia as regards army and unit strength or units in existence, as he is rarely specific about either. The third major source for the late army are the legal codes published in the East Roman empire in the 5th and 6th centuries: the Theodosian code (438) and the Corpus Iuris Civilis (528–39). These compilations of Roman laws dating from the 4th century contain numerous imperial decrees relating to all aspects of the regulation and administration of the late army.

Evolution of the 4th century army

Background: the Principate army

The regular army of the Principate was established by the founder–emperor Augustus (ruled 30 BCE – 14 CE) and survived until the end of 3rd century. The regular army consisted of two distinct corps, both being made up of mainly volunteer professionals.

The elite legions were large infantry formations, varying between 25 and 33 in number, of 5,500 men each (all infantry save a small cavalry arm of 120) which admitted only Roman citizens. The auxilia consisted of around 400 much smaller units of 500 men each (a minority were up to 1,000 strong), which were divided into approximately 100 cavalry alae, 100 infantry cohortes and 200 mixed cavalry/infantry units or cohortes equitatae. Some auxilia regiments were designated sagittariorum, meaning they contained only archers. The auxilia thus contained almost all the Roman army's cavalry and archers, as well as (from the late 1st century onwards) approximately the same number of foot soldiers as the legions. The auxilia were mainly recruited from the peregrini: provincial subjects of the empire who did not hold Roman citizenship, but the auxilia also admitted Roman citizens and possibly barbari, the Roman term for peoples living outside the empire's borders. At this time both legions and auxilia were almost all based in frontier provinces. The only substantial military force at the immediate disposal of the emperor was the elite Praetorian Guard of 10,000 men which was based in Rome.

The senior officers of the army were, until the 3rd century, mainly from the Italian aristocracy. Members of the senatorial order, the highest echelon, exclusively filled the following posts:

(a) legatus Augusti (provincial governor, who commanded military forces in the province as well as heading the civil administration)

(b) legatus legionis (legion commander)

(c) tribunus militum laticlavius (legion deputy commander).

The equites (or "knights"), the second order of nobility, provided:

(a) the governors of Egypt and a few other minor provinces

(b) the two praefecti praetorio (commanders of the Praetorian Guard)

(c) a legion's praefectus castrorum (3rd-in-command) and its remaining five tribuni militum (senior staff officers)

(d) the praefecti (commanders) of the auxiliary regiments.

Hereditary senators and equites normally combined military service with civilian posts, a career path known as the cursus honorum, typically starting with a period of junior administrative posts in Rome, followed by 5–10 years in the military and a final period of senior positions in the either the provinces or Rome.

Although the two aristocratic orders were hereditary, they were not closed to outsiders. Commoners could be elevated to equestrian, and equites to senatorial, rank by decree of the emperor, usually granted only to those attaining the minimum property qualification for each order. The property requirement for promotion was set by Augustus at 250,000 denarii, equivalent to the annual pay of 1,000 legionaries, for promotion from equites to senators and at 100,000 denarii for promotion to the order of equites. As an exception to the property requirement, the emperor customarily elevated the primuspilus (chief centurion) of each legion to equestrian rank on completion of his year in office. This resulted in some 30 career soldiers, often promoted from the ranks, joining the aristocratic order each year.

3rd century developments

The seminal development for the army in the early 3rd century was the Constitutio Antoniniana (Antonine Decree) of 212, issued by emperor Caracalla (r. 211–8). This granted Roman citizenship to all free inhabitants of the empire, ending the second-class status of the peregrini. This had the effect of breaking down the distinction between the citizen legions and the auxiliary regiments. It is uncertain whether the legions retained their elite status during the 3rd century. In the 1st and 2nd centuries, the legions were the symbol (and guarantors) of the dominance of the Italian "master nation" over its subject peoples. In the 3rd century, they were no longer socially superior to their auxiliary counterparts and the legions' very effective but expensive armour and equipment (e.g. the lorica segmentata) was phased out.

The traditional alternation between senior civilian and military posts fell into disuse in the 2nd and 3rd centuries, as the Italian hereditary aristocracy was replaced in the senior echelons of the army by the primipilares. In the 3rd century, only 10% of auxiliary prefects whose origins are known were Italian equestrians, compared to the majority in the previous two centuries. At the same time, equestrians increasingly replaced the senatorial order in the top commands. Septimius Severus (r. 197–211) placed equestrian primipilares in command of the three new legions he raised and Gallienus (260–8) did the same for all the other legions, giving them the title praefectus pro legato ("prefect acting as legate").

The early 3rd century also saw the steady build-up of the forces at the immediate disposal of the emperor, which became known as the comitatus ("escort", from which derives the English word "committee"). To the Praetorian Guard's 10,000 men, Septimius Severus added the legion II Parthica. Based at Albano Laziale near Rome, it was the first legion to be stationed in Italy since Augustus. In addition, he doubled the size of the imperial escort cavalry, the equites singulares Augusti, to 2,000 by drawing select detachments from alae on the borders. In total, his comitatus numbered some 17,000 men, equivalent to 31 infantry cohortes and 11 alae of cavalry. The trend for the emperor to gather round his person ever greater forces reached its peak in the 4th century under Constantine I the Great (ruled 312–37), whose comitatus may have reached 100,000 men, perhaps a quarter of the army's total effective strength. The primary function of the comitatus was not to serve as a strategic reserve, but rather as a deterrent against potential usurpation attempts. The disadvantage of a large comitatus was that it denuded the frontier provinces of a large number of elite regiments, weakening the empire's defence against barbarian incursions.

The rule of Gallienus saw the appointment of a senior officer, with the title of dux, to command all the comitatus cavalry. This force included some contingents of equites promoti (cavalry contingents detached from the legions), plus some apparently new Dalmatian light cavalry (equites Dalmatarum) and elements of allied barbarian cavalry (equites foederati). Under Constantine I, the head of the comitatus cavalry was given the title of magister equitum ("master of horse"), which in Republican times had been held by the deputy to a Roman dictator. But neither title implies the existence of an independent "cavalry army", as was suggested by some more dated scholars. Both forces were integral parts of mixed infantry and cavalry comitatus, with the infantry remaining the predominant element.

The 3rd century saw a progressive reduction in the size of the legions and even some auxiliary units. Legions were broken up into smaller units, as evidenced by the shrinkage of the British legions and the abandonment of their traditional large bases. In addition, from the 2nd century onwards, the separation of some detachments from their parent units became permanent in some cases, establishing new unit types e.g. the vexillatio equitum Illyricorum based in Dacia in the early 2nd century and the equites promoti and numerus Hnaufridi in Britain. This led to the proliferation of unit types in the 4th century, generally of smaller size than those of the Principate. For example, in the 2nd century, vexillatio (from vexillum = "standard") was originally a generic term meaning any detachment from a legion or auxiliary regiment, either cavalry or infantry. In the 4th century, it denoted an elite cavalry regiment.

In the 3rd century, a small number of regular units are recorded as bearing the names of barbarian tribes (as opposed to peregrini tribal names) for the first time. These were clearly foederati (allied troops under a military obligation to Rome) converted into regular units, a trend that was to accelerate in the 4th century. The ala I Sarmatarum, for example, based in Britain, probably composed of some of the 5,500 captured Sarmatian horsemen sent to garrison Hadrian's Wall by emperor Marcus Aurelius in 175.

3rd century crisis

File:104 Claudius II Gothicus.jpg

The Illyrian emperor Claudius II (r. 268–70), whose annihilating victories over the barbarian invaders of the empire saved it from collapse. Claudius was the first in a line of Illyrian emperors that were to rule the empire for a century. Debased silver antoninianus

Emperor Aurelian (270–5), who completed Claudius' expulsion of barbarian invaders. He built the City of Rome's first set of walls since the Servian Wall 650 years earlier

The emperor Diocletian (ruled 284–305), who launched wide-ranging reforms of the Roman army and government. Bronze follis coin

The Tetrarchs: Diocletian and his three colleagues. To the left, the two Augusti (co-emperors), to the right the two Caesars (deputy emperors). Note the Pannonian caps popularised by the Illyrian officer class of the Roman army; and the sword grips with eagle-head pommels. Porphyry statue on Basilica di San Marco, Venice

The emperor Constantine I (ruled 312–37), who established the first large-scale comitatus (imperial escort army) and divided the army into escort army (comitatenses) and border (limitanei) troops, giving the late Roman army the structure described in the Notitia Dignitatum. Bust in Musei Capitolini, Rome

The mid 3rd century saw the empire plunged into a military and economic crisis which almost resulted in its disintegration. It consisted of a series of military catastrophes in 251–271 when Gaul, the Alpine regions and Italy, the Balkans and the East were simultaneously overrun by Alamanni, Sarmatians, Goths and Persians respectively. At the same time, the Roman army was struggling with the effects of a devastating pandemic, probably of smallpox, the Plague of Cyprian which began in 251 and was still raging in 270, when it claimed the life of emperor Claudius II Gothicus (268–70). The evidence for the earlier Antonine pandemic of the late 2nd century, also smallpox, indicates a mortality of 15–30% in the empire as a whole. Zosimus describes the Cyprianic outbreak as even worse. The armies would likely have suffered deaths at the top end of the range, due to their close concentration of individuals and frequent movements across the empire.

The 3rd century crisis started a chain-reaction of socio-economic effects that proved decisive for the development of the late army. The combination of barbarian devastation and reduced tax-base due to plague bankrupted the imperial government, which resorted to issuing ever more debased coin: the antoninianus, the silver coin used to pay the troops in this period, lost 95% of its silver content between its launch in 215 and its demise in the 260's. This inevitably led to rampant price inflation: the price of wheat under Diocletian was 67 times the typical Principate figure. The monetary economy collapsed and the army was obliged to rely on food levies obtain sufficient supplies. Soldiers' salaries became virtually worthless, reducing the army's peasant recruits, once well-paid with plenty of disposable income, to a subsistence-level drudgery no better than the agriculture they came from. This forced the government to rely on conscription to find enough recruits. But even this was not sufficient to plug the recruitment shortfalls caused by the plague. The only solution was large-scale recruitment of barbarians into the regular army. By the mid-4th century, barbarians probably accounted for about a quarter of all recruits (and over a third in elite regiments), likely a far higher share than in the 1st/2nd centuries.

Illyrian military junta

The Illyrian-speaking tribes that dominated the Roman provinces of Pannonia, Dalmatia and Moesia Superior, and included mountain tribes of semi-nomadic pastoralists such as the Dalmatae and Breuci, had a fearsome reputation as warriors. They were seen as excellent soldier material. From the time of Domitian (r. 81–96), when over half the Roman army was deployed in the Danubian regions, the Illyrian provinces had been the most important recruiting ground of the auxilia and later the legions. In the 3rd century, Romanised Illyrians came to dominate the army's senior officer echelons.

Finally, the Illyrian officer class seized control of the state itself. In 268, the emperor Gallienus (r. 260–8) was overthrown by a coup d'état organised by a clique of Illyrian senior officers, including his successors Claudius II Gothicus and Aurelian (270–5). They and their successors Probus (276–8) and Diocletian (r. 284–305) and his colleagues in the Tetrarchy formed a sort of self-perpetuating military junta of Illyrian officers who were born in the same provinces (several in the same city, Sirmium, a major legionary base in Moesia Superior) or had served in the same regiments.

The junta succeeded in reversing the military disasters of 251–71 with a string of brilliant victories. Claudius II acquired his title Gothicus by a crushing defeat inflicted on a vast Gothic army trying to leave the empire laden with its spoils (Battle of Naissus, 268). The Goths did not seriously threaten the empire again until a century later at Adrianople (378). A few months later, it was the turn of the Alamanni invaders in Italy, who were annihilated at the Battle of Lake Benacus (268). Claudius' deputy and successor Aurelian went on to despatch the Sarmatians and another Alamanni force in 270.

The Illyrian emperors continued to rule the empire until 379. Indeed, until 364, power was held by descendants of one of the original junta members. Constantine I' s father, Constantius Chlorus was a Caesar (deputy emperor) in Diocletian's Tetrarchy. Constantine I's sons ruled after his death in 337 until the death of Julian in 363. After that the empire was ruled by the sons (Valentinian I and Valens) and grandson (Gratian) of another Illyrian senior officer, (Gratian the Elder), who was born under Diocletian.

The junta restored the army to its former strength and effectiveness. But the Illyrian emperors had a narrow political focus, solely concerned with the needs and interests of the military. Under them, the empire as a whole was subordinated to serve the army, rather than the other way round. They were also divorced from the immensely wealthy Roman senatorial families that continued to dominate the Senate and owned much of the empire's land. This in turn bred a feeling of alienation from the army among the Roman aristocracy which in the later 4th century began to resist the military's exorbitant demands for recruits and supplies.

Diocletian

Diocletian's wide-ranging administrative and military reforms were entirely aimed at providing the military with sufficient resources, both in manpower and supplies, and to strengthening border defences.

To deal with the perennial problem of usurpers which repeatedly plunged the empire into civil war at immense cost in lives and treasure and were a greater danger to the empire than barbarian invasions, and also to address the problem that the empire was too vast to be governed effectively by one man, he instituted the Tetrarchy. This divided the empire into two halves, East and West, each to be ruled by an Augustus (emperor); each Augustus would in turn appoint a deputy called a Caesar, who would act both as his second-in-command and designated successor. This four-man team would thus have the flexibility to deal with multiple and simultaneous challenges, while also providing a legitimate succession. The system certainly did not prevent usurpations and civil wars, as the career of Constantine I demonstrates: he was himself a usurper and fought major wars against his rivals Maxentius and Licinius. But its core feature, the division of the empire into Eastern and Western halves, each governed by an equal co-emperor, proved enduring.

Diocletian reformed the provincial administration, dividing the provinces into smaller units to allow greater control, grouped together into divisions called dioceses, in turn under a praefectus praetorio (the same title as the commanders of the Praetorian Guard), who was also the supreme commander of army units in the dioceses. Diocletian instituted the system of indictiones (tax demands issued in advance of the tax cycle), with the amount of tax demanded related to the amount of cultivated land in each province, aimed at making more efficient and more equitable the collection of taxes in kind. To deal with the problem of rural depopulation (and consequent loss of food production), he decreed that peasants must register in their home locality and never leave it. (This measure was the origin of the medieval system of villeins i.e. serfs tied to the land). In the words of one historian, "Diocletian... turned the entire empire into a regimented logistic base" (to supply the army). Diocletian completed the exclusion of the senatorial class, still dominated by the Italian aristocracy, from all senior military commands and all top administrative posts except in Italy.

He also divorced military from civil command in some cases. The old legatus Augusti (governor) of the Principate had combined the role of administrative head with that of military commander-in-chief of forces in his province. Now, command of troops in some provinces were entrusted to purely military officers called duces limitis ("border commanders", singular form dux, literally "leader": the origin of the medieval noble rank of duke). However, this was not universally applied. In many provinces, the governor remained in command.

The division of the empire among four Tetrarchs (each with his own court), the progressive split between civil and military administration, the proliferation of provinces (tripled to 250) and their superstructure of dioceses and praetorian prefectures, and the elaborate system of levies of recruits and supplies for the army led to explosive growth in the imperial bureaucracy. The Principate had been a remarkably slimline administration, with just 250 senior officials running the vast empire, relying on local government and private contractors to deliver the necessary taxes and services. But though few, these officials drew huge salaries, so their total cost was considerable (ca. 7 % of the total state budget). By the time of the Notitia, comparable positions had grown to ca. 6,000, a 24-fold increase. Admittedly, late high officials were paid far less than in the Principate, perhaps an average of a tenth as much. Even so, the late bureaucracy would have been around two and a half times as expensive overall, swallowing substantial resources. The annual cost of the Principate bureaucracy has been estimated at ca. 750,000 aurei (= 1.125 million Diocletianic solidi). Therefore the additional cost of the late bureaucracy would have totalled ca. 1.7 m solidi, enough to pay 400,000 troops each an extra 4.2 solidi per annum, doubling or tripling their bonus payments and bringing their pay back up to 2nd century levels.

The late army was therefore unable to attract sufficient high-quality volunteers (except barbarians) as in the Principate and was obliged to rely heavily on reluctant and often poor-quality conscripts. Diocletian appears to have instituted systematic annual conscription for the first time since the days of the Roman Republic. In addition he is probably responsible for the decree, first recorded in 313, obliging the sons of serving soldiers (and officers) or veterans to enlist.

Under Diocletian, the number of legions, and probably of other units, appears to have more than doubled. But it is unlikely that overall army size increased nearly as much, since unit strengths appear to have been reduced, in some cases drastically. For example, there are legions in the mid-4th century that are documented with just 1,000 effectives, less than a fifth of their 2nd-century strength. Diocletian and his three colleagues also each had a comitatus at their disposal. But under Diocletian, these remained informal and small in size and relied on reinforcements from frontier forces for major operations. Numbers "in the time of Diocletian" are given as 390,000 (excluding fleets and foederati) by a 6th-century writer, although it is unclear whether this was at the start or end of his rule, or, as the wording implies, sometime during it. It is generally agreed that Diocletian increased army numbers substantially, but it is impossible to say with certainty by how much.

Even more than increasing the size of the army, Diocletian's efforts and resources were focused on a massive upgrading of the defensive infrastructure along all the empire's borders, including new forts and strategic military roads. There is abundant archaeological and epigraphic evidence of this work, especially on the desert frontiers of Arabia and North Africa.

Constantine

Constantine I probably completed the replacement of provincial governors as commanders of military units in their provinces by duces. The Praetorian prefects lost their military command and became purely administrative officials, whose central and vital role was to ensure that the armies in their circumscription were properly supplied.

After defeating Maxentius in 312, Constantine disbanded the Praetorian Guard, ending the latter's 300-year existence. Although the instant reason was the Guard's support for his rival Maxentius, a force based in Rome had also become obsolete since emperors now rarely resided there.

Constantine expanded his comitatus into a major and permanent force. This was achieved by the addition of units withdrawn from the frontier provinces and by creating new units: more cavalry vexillationes and new-style infantry units called auxilia. The expanded comitatus was now placed under the command of two new officers, a magister peditum to command the infantry and magister equitum for cavalry. Comitatus troops were now formally denoted comitatenses to distinguish them from the frontier forces (limitanei). The size of the Constantinian comitatus is uncertain. But Constantine mobilised 98,000 troops for his war against Maxentius, according to Zosimus. It is likely that most of these were retained for his comitatus. This represented about a quarter of the total regular forces, if one accepts that the Constantinian army numbered around 400,000.

In addition, Constantine appears to have reorganised the border forces along the Danube, replacing the old-style alae and cohortes with new units of cunei (cavalry) and auxilia (infantry) respectively. It is unclear how the new-style units differed from the old-style ones, but those stationed on the border (as opposed to those in the comitatus) may have been smaller, perhaps half the size. In sectors other than the Danube, old-style auxiliary regiments survived.

The 5th century historian Zosimus strongly criticised the establishment of the large comitatus, accusing Constantine of wrecking his predecessor Diocletian's work of strengthening the border defences: "By the foresight of Diocletian, the frontiers of the Roman empire were everywhere studded with cities and forts and towers... and the whole army was stationed along them, so it was impossible for the barbarians to break through... But Constantine ruined this defensive system by withdrawing the majority of the troops from the frontiers and stationing them in cities which did not require protection."

Zosimus' critique is probably excessive, both because the comitatus already existed in Diocletian's time and because some new regiments were raised by Constantine for his expanded comitatus, as well as incorporating existing units. Nevertheless, the majority of his comitatus was drawn from existing frontier units. This drawdown of large numbers of the best units inevitably increased the risk of successful large-scale barbarian breaches of the frontier defences.

It was probably this factor that led to the emergence of comitatus based in frontier regions (the regional comitatus), distinct from the comitatus praesentales escorting the emperor(s). From the defeat of the usurper Magnentius in 353, there appears to have always been a comitatus in Gaul and one in the East, each under a magister equitum, and one in Illyricum under a senior comes rei militaris (literally "companion for military affairs", the origin of the medieval noble rank of count), irrespective of where the emperor(s) were. These regional armies became steadily more numerous until, by the time of the Notitia, there were three in the East and six in the West. Their evolution was a partial reversal of Constantine's policy and, in effect, a vindication of Zosimus' critique that the limitanei forces had been left with insufficient support. But the imperial escort armies remained in existence, and in ca. 420 the three comitatus praesentales listed in the Notitia, each 20–30,000 strong, still contained a total of ca. 75,000 men. If one accepts that the army at the time numbered about 350,000 men, the escort armies still contained 20–25% of the total effectives.

Army size

The traditional view of scholars is that the 4th century army was much larger than the 2nd century army, in the region of double the size. The late 6th century writer Agathias, gives a global total of 645,000 effectives for the army "in the old days", presumed to mean at its peak under Constantine I. This figure probably includes fleets, giving a total of ca. 600,000 for the army alone. A.H.M. Jones' Later Roman Empire (1964), which contains the fundamental study of the late Roman army, calculated a similar total of 600,000 (exc. fleets) by applying his own estimates of unit strength to the units listed in the Notitia Dignitatum.

But the Agathias-Jones view has fallen out of favour with some historians in more recent times. Agathias' figure, if it has any validity at all, probably represents the official, as opposed to actual strength of the Constantinian army. In reality, late units were in practice severely under-strength. The available evidence for the 4th century indicates that actual numbers may have been on average only about two-thirds of official. Thus Agathias' 600,000 on paper probably were not more than ca. 400,000 in reality. The latter figure accords well with the other global figure from ancient sources, that of the 6th century writer John Lydus of 389,704 (excluding fleets) for the army of Diocletian. Lydus' figure is accorded greater credibility than Agathias' by scholars because of its precision (implying that it was found in an official document) and the fact that it is ascribed to a specific time period. Indeed it is possible that Agathias' figure represents the official strength of the late army while Lydus is the actual strength in Diocletian's time.

Jones' figure of 600,000 is based on assumptions about unit strengths which are probably too high. This especially concerns limitanei units (there is less dispute about the size of comitatus units, for which there is more available evidence). Jones calculated unit strengths in Egypt under Diocletian using papyrus evidence of unit payrolls. But a rigorous reassessment of the evidence by R. Duncan-Jones concluded that Jones had overestimated unit sizes by 2–6 times. For example, Jones estimated legions on the frontiers at ca. 3,000 men. But Duncan-Jones' revisions and other evidence suggest that frontier legions probably did not exceed 500.

The size of the late army was thus probably much closer to the Lydus figure of ca. 400,000 than to Agathias' 600,000. At the same time, more recent work on the auxilia of the Principate has suggested that the regular army was considerably larger than the ca. 300,000 traditionally assumed. This is because the 2nd century auxilia was not equal in numbers to the legions as in the early 1st century, but some 50% larger. The Principate army probably reached a peak of nearly 450,000 (excluding fleets and foederati) in the early 3rd century. Furthermore, the evidence is that the actual strength of 2nd century units was typically much closer to official (ca. 85%). It is therefore unlikely that the 4th century army ever significantly exceeded the 2nd century army in size.

ROMAN ARMY NUMBERS 24–337

Army corps	Tiberius 24	Hadrian ca. 130	S. Severus 211	Diocletian start 284	Diocletian 284–305	Constantine I end rule 337	Notitia ca. 420
LEGIONS	125,000	155,000	182,000
AUXILIA	125,000	218,000	250,000
PRAETORIAN GUARD	~~5,000	~10,000	~10,000
Total Roman Army	255,000	383,000	442,000	350,000?	390,000	410,000	350,000?

NOTE: Figures exclude Roman navy effectives and barbarian foederati units.

Army structure

The later 4th century army contained three types of army group: (a) imperial escort armies (comitatus praesentales). These were ordinarily based near the imperial capitals (Milan in the West, Constantinople in the East), but usually accompanied the emperors on campaign. (b) Regional field armies (comitatus). These were based in strategic regions, on or near the frontiers. (c) Border armies (exercitus limitanei).

Types (a) and (b) are both frequently defined as "mobile field armies". This is because, unlike the limitanei units, they were not based in fixed locations. But their strategic role was quite different. The escort armies' primary role was to provide the emperor's ultimate insurance against usurpers: the very existence of such a powerful force would deter many potential rivals, and if it did not, the escort army alone was often sufficient to defeat them. Their secondary role was to accompany the emperor on major campaigns such as a foreign war or to repel a large barbarian invasion. The regional comitatus, on the other hand, had the task of supporting the limitanei in operations in the region they were based in.

Command structure

File:Late roman army.svg

High command structure of the East Roman army ca. 395. Based on the Notitia Dignitatum. Troop numbers based on recent unit size estimates. Reporting structure as in Jones (1964) 100 and 609

File:Late West Roman army.svg

High command structure of the West Roman army ca. 410–425. Based on the Notitia Dignitatum. Troop numbers based on recent unit size estimates.

The command structures of the Eastern and Western armies of the empire, as recorded in the Notitia Dignitatum, are represented diagramatically in the organisation charts (right). The eastern section of the Notitia is dated to ca. 395, at the death of Theodosius I. The western section was completed later, in the 420's, after the West had been overrun by barbarian tribes.

By the end of the 4th century, there were three comitatus praesentales: two in the East and one in the West. The two Eastern armies wintered near Constantinople at Nicaea and Nicomedia and the Western army was usually based in the Po valley near Milan. Each was commanded by a magister militum ("master of soldiers", the highest military rank, also known as magister peditum or equitum: these titles had lost their literal meaning and were no longer related to infantry or cavalry). Each magister was assisted by a deputy called a vicarius.

In the East, there were three major regional comitatus, also with apparently settled winter bases: Oriens (based at Antioch), Thraciae (Marcianopolis), Illyricum (Sirmium) plus two smaller forces in Aegyptus (Alexandria) and Isauria. The large comitatus were commanded by magistri, the two smaller ones by comites rei militaris. All five reported direct to the eastern Augustus, according to the Notitia. But 5th century laws imply that the two comites were subordinate to the magister militum per Orientem. This structure remained essentially intact in the East Roman army until the 6th century.

In the West, there were six regional comitatus. By far the largest was in Gaul (Trier), under a magister equitum (literally "master of cavalry", although his army was composed mainly of infantry). The others were in West Illyricum (Sirmium), Britain, Spain, Tingitania and Africa, all under comites. All these officers reported to the magister in Italy, who was effectively supreme commander of the Western army. However, the Western section of the Notitia Dignitatum was drawn up in the chaotic conditions caused by the great barbarian invasion of Gaul in 406 and reflects the ascendancy of the half–barbarian military strongman Stilicho, who was appointed by Theodosius I as guardian of his infant son and successor Honorius. It therefore represents a reporting structure and force distribution that was probably very different from that of 350 to 395. It appears that in the earlier era, both magistri reported direct to the emperor, but whether the comites also did so is uncertain. There is some evidence that the two comites in Britain may have been subordinate to the magister equitum in Gaul e.g. Julian's despatch of magister equitum Lupicinus to deal with barbarian trouble in Britain in 360. As regards force distribution, it is evident that the duces in Gaul have been stripped of troops to reinforce the magister equitum 's comitatus and would previously have disposed of much larger forces. Similarly, the British garrison of ca. 18,000 men (which must refer to the period ante 410, when the Roman army finally evacuated the island) was probably much larger earlier in the 4th century, but had been denuded of troops by successive usurpers.

Under Diocletian, the duces limitis (border commanders) reported to the praefectus praetorio of their diocese. When the latter were stripped of their military command under Constantine, the duces may have reported to the magistri of the imperial escort armies. From at least the 360's onwards, however, they reported to the magister militum or comes in command of their regional comitatus.

Regiments

The changes to unit structure in the 4th century were reduction of unit sizes and increase in unit numbers, establishment of new unit types and establishment of a hierarchy of units more complex than the old one of legions and auxilia.

Regiments were classified in four grades, which denoted quality, prestige and probably pay: scholares, palatini, comitatenses and limitanei. The scholares were the members of the elite scholae cavalry regiments that formed the imperial horseguards. The palatini (literally: "of the palace") were regiments mostly (originally only) deployed in the imperial escort armies (exercitus praesentales). The comitatenses were regiments mostly present in the regional comitatus, although the term was also used loosely to include the palatini. (The latter were only differentiated when the regional comitatus were established). Finally, the limitanei referred to regiments in the ducal border forces.

The evidence for the strength of late army units is very fragmented and equivocal. The table below gives some recent estimates of unit strength, by unit type and grade:

ESTIMATED SIZE OF REGIMENTS IN 4th CENTURY ARMY

Cavalry unit type	Comitatenses (inc. palatini)	Limitanei	XXXXX	Infantry unit type	Comitatenses (inc. palatini)	Limitanei
Ala		120–500		Auxilium	400–800
Cuneus		200–300		Cohors		160–500
Equites		80–300		Legio	800–1,200	500–1,000
Schola	500			Milites		200–300
Vexillatio	400–600			Numerus		200–300

Much uncertainty remains, especially regarding the size of limitanei regiments, as can be seen by the wide ranges of the size estimates. It is also possible, if not likely, that unit strengths changed over the course of the 4th century. For example, it appears that Valentinian I split about 150 comitatus units with his brother and co-emperor Valens. The resulting units may have been just half the strength of the parent units (unless a major recruitment drive was held to bring them all up to original strength).

In the comitatus, there is consensus that vexillationes were ca. 500 and legiones ca. 1,000 strong. The greatest uncertainty concerns the size of the crack auxilia palatina infantry regiments, originally formed by Constantine. Ammianus twice mentions detachments of 300 men from unspecified comitatus units. It is likely that at least one of these was an auxilium, implying a total unit size substantially in excess of that figure. A force of six infantry units sent to Honorius totaled 4,000 men. If all these units were auxilia, that would imply a unit size of ca. 700. But the force may have included two legiones of ca. 1,000 each, since it was customary to mix the two types of unit in task forces and for units to operate in pairs. If so, an auxilium would number ca. 500 men, which draws support from its similarity to the size of its predecessor, the auxiliary cohors. On the other hand, Honorius withdrew five units from Dalmatia totalling 6,000 men, implying that each unit averaged 1,200 men. If this force included auxilia, it would imply the latter were of similar size to legiones. But Jones suggests that it contained only legiones. Also this force may have included cavalry e.g. a large numerus of barbarian allied cavalry, which would distort the figures.

For the size of limitanei units, opinion is divided. Jones and Elton suggest from the literary evidence that they contained ca. 500 men each. Others draw on papyrus and recent archaeological evidence to argue that these units averaged perhaps half that strength (ca. 250). It is this discrepancy that is largely responsible for the wide range of estimates, of between 400,000 and 600,000 for the late army as a whole, as the assumed unit sizes have been multiplied by the number of units listed in the Notitia to arrive at an overall estimate.

Scholae

Shield insignia of regiments under the command of the Magister Militum Praesentalis II of the East Roman army c. 395. Page from the Notitia Dignitatum, a medieval copy of a Late Roman register of military commands

The Scholae palatinae were elite cavalry regiments that acted as imperial escorts and replaced the equites singulares Augusti, the cavalry wing of the Praetorian Guard of the Principate. They existed in Constantine's time and may have been founded by Diocletian. At the end of the 4th century, there were five scholae regiments (2,500 men) under the western Augustus and seven (3,500) in the East. This compares with 2,000 equites singulares in the late 2nd century. They were outside the normal military chain of command as they did not belong to the comitatus praesentales and reported to the magister officiorum, a civilian official. However, this was probably only for administrative purposes. On campaign, the tribunes (regimental commanders) of the scholae probably reported direct to the emperor himself. 40 select troops from the scholae, called candidati from their white uniforms, acted as the emperor's personal bodyguards.

Comitatenses (inc. palatini)

In the comitatus armies (both escort and regional) cavalry regiments were known as vexillationes, infantry regiments as either legiones or auxilia.

The majority of Roman cavalry regiments in the comitatus (61%) remained of the traditional semi-armoured type, similar in equipment and tactical role to the alae of the Principate and suitable for mêlée combat. These regiments carry a variety of titles: comites, equites scutarii, equites stablesiani or equites promoti. These titles are probably purely traditional, and do not indicate different unit types or functions. 24% of regiments were unarmoured light cavalry, denoted equites Dalmatae, Mauri or sagittarii (mounted archers), suitable for harassment and pursuit. Mauri light horse had served Rome as auxiliaries since the Second Punic War 500 years before. Equites Dalmatae, on the other hand, seem to have been regiments first raised in the 3rd century. 15% of regiments were heavily armoured cavalry (cataphracti and clibanarii), suitable for the shock charge.

Infantry regiments mostly fought in close order as did their Principate forbears. Infantry equipment was broadly similar to the that of auxiliaries in the 2nd century, with some modifications (see Equipment, below).

About 100 regiments in the Notitia, mostly palatini, have the same name, but are designated seniores or iuniores e.g. equites Batavi seniores and equites Batavi iuniores. The timing, origin and significance of the new titles are uncertain. The first documented use of the titles was in 356 (epitaph for a soldier of the Ioviani Cornuti Seniores). Most likely, however, this naming convention was first used extensively under Valentinian I (364–75). In any case, the titles appear to have reflected precedence, rather than any significant difference in quality.

Another feature of comitatenses units was the pairing of regiments to form a brigade, under the command of a junior comes (denoted here "junior", to distinguish from comes rei militaris, a far senior officer that commanded a regional comitatus). Such brigades would always operate and transfer together e.g. the legions Ioviani and Herculiani or the auxilia palatina Heruli and Petulantes.

Limitanei

In the ducal border forces, most types of regiment were present. For infantry, there are regiments called milites, numeri and auxilia as well as old-style legiones and cohortes. Cavalry regiments are called equites, cunei and old-style alae.

The evidence is that comitatenses regiments were considered of higher quality than limitanei. But the difference should not be exaggerated. Suggestions have been made that the limitanei were a part-time militia of local farmers, of poor combat capability. This is almost certainly mistaken. In reality, limitanei were full-time professionals. Indeed, it was forbidden by law for them to work in the fields or herd animals. The limitanei were charged with combating the incessant small-scale barbarian raids that were the empire's enduring security problem. It is therefore likely that their combat readiness and experience were high. This was demonstrated at the siege of Amida (359) where the besieged frontier legions resisted the Persians with great skill and tenacity. Limitanei regiments often joined the comitatus for specific campaigns, sometimes being kept on long-term with the title pseudocomitatenses.

Specialists

Archer units are denoted in the Notitia by the term equites sagittarii (mounted archers) and sagittarii (foot archers, from sagitta = "arrow"). As in the Principate, it is likely that many non-sagittarii regiments also contained some archers. Mounted archers appear to have been exclusively in light cavalry units. Archer units, both foot and mounted, were present in the comitatus. In the ducal forces, only mounted archers are listed in the Notitia, which may indicate that many limitanei infantry regiments contained their own archers.

A distinctive feature of the late army is the appearance of independent units of artillery, which during the Principate appears to have been integral to the legions. Called ballistarii (from ballista = "catapult"), seven such units are listed in the Notitia, all but one belonging to the comitatus. But a number are denoted pseudocomitatenses, implying that they originally belonged to the ducal forces. The purpose of independent artillery units was presumably to permit heavy concentration of firepower, especially useful for sieges. However it is likely that many ordinary regiments continued to possess integral artillery, especially in the ducal forces.

The Notitia lists a few units of presumably light infantry with names denoting specialist function: superventores ("interceptors"), exculcatores ("trackers"), exploratores ("scouts"). At the same time, Ammianus describes light-armed troops with various terms: velites, leves armaturae, exculcatores, expediti. It is unclear from the context whether any of these were independent units, specialist sub-units, or indeed just detachments of ordinary troops specially armed for a particular operation. The Notitia evidence implies that, at least in some cases, Ammianus could be referring to independent units.

Accommodation

Comitatus troops and border troops had different accommodation arrangements. Most border units were based in forts as were their predecessors, the auxiliary regiments of the Principate (indeed, in the same forts, in many cases). Some of the larger limitanei units (legiones and vexillationes) were based in cities, probably in permanent barracks.

Comitatus troops were also based in cities (when not on campaign: then they would be in temporary camps). But it seems that did not usually occupy purpose-built accommodation like the city-based limitanei. From the legal evidence, it seems they were normally compulsorily billeted in private houses (hospitalitas). This is because they often wintered in different provinces: the comitatus praesentales accompanied their respective emperors on campaign. However, in the 5th century, emperors campaigned more rarely in person, so the praesentales became more static in their winter bases.

Recruitment

Romans

During the Principate, it appears that most recruits, both legionary and auxiliary, were volunteers (voluntarii). Compulsory conscription (dilectus) was never wholly abandoned, but was generally only used in emergencies or before major campaigns when large numbers of additional troops were required. In marked contrast, the late army relied mainly on compulsion for its recruitment of Roman citizens. Firstly, the sons of serving soldiers (and officers) or veterans were required by law to enlist. Secondly, a regular annual levy was held based on the indictio (land tax assessment). Depending on the amount of land tax due on his estates, a landowner (or group of landowners) would be required to provide a commensurate number of recruits to the army. Naturally, landowners had a strong incentive to keep their best young men to work on their estates, sending the less fit or reliable for military service. There is also evidence that they tried to cheat the draft by offering the sons of soldiers (who were liable to serve anyway) and vagrants (vagi) to fulfil their quota.

However, the recruitment base was in practice not universal. Firstly, a land-based levy meant recruits were exclusively the sons of peasants, as opposed to townspeople. Thus some 20% of the empire's population was excluded. In addition, as during the Principate, slaves were not admissible. Nor were freedmen and persons in certain occupations such as bakers and innkeepers. In addition, provincial officials and curiales (city council members) could not enlist. These rules were relaxed only in emergencies, as during the military crisis of 405–6 (Radagaisus' invasion of Italy and the great barbarian invasion of Gaul). Most importantly, the conscription requirement was often commuted into a cash levy, at a fixed rate per recruit due. This was done for certain provinces, in certain years, although the specific details are largely unknown. It appears that conscription was not applied evenly across provinces but concentrated heavily in the army's traditional recruiting areas of Gaul (including the two Germaniae provinces along the Rhine) and the Danubian provinces, with other regions presumably often commuted. An analysis of the known origins of comitatenses in the period 350–476 shows that in the Western army, the Illyricum and Gaul dioceses together provided 52% of total recruits. On the other hand, only 7% were Italians despite Italy probably being the most populous diocese of the West. In the Eastern army, the Danubian dioceses of Dacia and Thracia provided 54% of the total. Overall the Danubian regions provided nearly half of the whole army's recruits, despite containing only three of the 13 dioceses. This picture is much in line with the 2nd century position.

Prospective recruits had to undergo an examination. Recruits had to be 20–25 years of age, a range that was extended to 19–35 in the later 4th century. Recruits had to be physically fit and meet the traditional minimum height requirement of 6 Roman feet (5ft 10in, 175cm) until 367, when it was reduced to 5 Roman feet and 3 Roman palms (5ft 7in, 167cm).

Once a recruit was accepted, he was branded to facilitate recognition if he attempted to desert. The recruit was then issued with an identification disk (which was worn around the neck) and a certificate of enlistment (probatoria). He was then assigned to a unit. A law of 375 required those with superior fitness to be assigned to the comitatenses. A law of Constantine decreed that the son of a cavalryman had the right to enrol in a cavalry regiment if he brought his own horse. In the 4th century, the minimum length of service was 20 years (24 years in some limitanei units). This compares with 25 years in both legions and auxilia during the Principate.

The widespread use of conscription, the compulsory recruitment of soldiers' sons, the relaxation of age and height requirements and the branding of recruits all add up to a picture of an army that had severe difficulties in finding, and retaining, sufficient recruits. Recruitment difficulties are confirmed in the legal code evidence: there are measures to deal with cases of self-mutilation to avoid military service (such as cutting off a thumb), including an extreme decree of 386 requiring such persons to be burnt alive. Desertion was clearly a serious problem, and was probably much worse than in the Principate army, since the latter was mainly a volunteer army. This is supported by the fact that the granting of leave of absence (commeatus) was more strictly regulated. While in the 2nd century, a soldier's leave was granted at the discretion of his regimental commander, in the 4th century, leave could only be granted by a far senior corps commander (dux, comes or magister militum). Against this, Elton argues that there were no serious recruitment problems, based on the extensive exemptions to military service granted. But Elton admits that while the official strength of comitatus units was 600 for cavalry units and 1,200 for infantry units, their actual recorded strength was 400 and 800 respectively. The massive disparity between official and actual strength is powerful evidence of recruitment problems.

Barbarians

Barbari ("barbarians") was the generic term used by the Romans to denote peoples resident beyond the borders of the empire, and best translates as "foreigners" (it is derived from a Greek word meaning "to babble": a reference to their outlandish tongues).

Most scholars believe that the regular auxilia recruited significant numbers of barbari throughout their history. However, there is little evidence of this before the 3rd century: the scant evidence suggests that the vast majority, if not all, of auxilia were Roman peregrini (second-class citizens) or Roman citizens. In any case, the 4th century army was probably much more dependent on barbarian recruitment than its 1st/2nd century predecessor. The evidence for this may be summarised as follows:

1. The Notitia lists a number of barbarian military settlements in the empire. Known as laeti or gentiles ("natives"), these were an important source of recruits for the army. Groups of Germanic or Sarmatian tribespeople were granted land to settle in the Empire, in return for military service. Most likely each ommunity was under a treaty obligation to supply a specified number of troops to the army each year. The resettlement within the empire of barbarian tribespeople in return for military service was not a new phenomenon in the 4th century: it stretches back to the days of Augustus. But it does appear that the establishment of military settlements was more systematic and on a much larger scale in the 4th century.
2. The Notitia lists a large number of units with barbarian names. This was probably the result of the transformation of irregular allied units serving under their own native officers (known as socii, or foederati) into regular formations. During the Principate, regular units with barbarian names are not attested until the 3rd century and even then rarely e.g. the ala I Sarmatarum attested in 3rd century Britain, doubtless an offshoot of the Sarmatian horsemen posted there in 175.
3. The emergence of significant numbers of senior officers with barbarian names in the regular army, and eventually in the high command itself. In the early 5th century, the Western Roman forces were often controlled by barbarian-born generals, such as Arbogast, Stilicho and Ricimer.
4. The adoption by the 4th century army of barbarian (especially Germanic) dress, customs and culture, suggesting enhanced barbarian influence. For example, Roman army units adopted mock barbarian names e.g. Cornuti = "horned ones", a reference to the German custom of attaching horns to their helmets, and the barritus, a German warcry. Long hair became fashionable, especially in the palatini regiments, where barbarian-born recruits were numerous.

Quantification of the proportion of barbarian-born troops in the 4th century army is highly speculative. Elton has the most detailed analysis of the meagre evidence. According to this, about a quarter of the sample of army officers was barbarian-born in the period 350–400. Analysis by decade shows that this proportion did not increase over the period, or indeed in the early 5th century. The latter trend implies that the proportion of barbarians in the lower ranks was not much greater, otherwise the proportion of barbarian officers would have increased over time to reflect that.

If the proportion of barbarians was in the region of 25%, then it is probably a much higher proportion than in the 2nd century regular army. If the same proportion had been recruited into the auxilia of the 2nd century army (the legions were closed to non-citizens), then in excess of 40% of recruits would have been barbarian-born, since the auxilia constituted 60% of the regular land army. There is no evidence that recruitment of barbarians was on such a large scale in the 2nd century.

An analysis of named soldiers of non-Roman origin shows that 75% are Germanic: Franks, Alamanni, Saxons, Goths, and Vandals are attested in the Notitia unit names. Other significant sources of recruits were the Sarmatians from the Danubian lands; and Armenians, and Iberians from the Caucasus region. In contrast to Roman recruits, the vast majority of barbarian recruits were probably volunteers, drawn by conditions of service and career prospects that to them probably appeared desirable, in contrast to their living conditions at home. A minority of barbarian recruits were enlisted by compulsion, namely dediticii (barbarians who surrendered to the Roman authorities, often to escape strife with neighbouring tribes) and tribes who were defeated by the Romans, and obliged, as a condition of peace, to undertake to provide a specified number of recruits annually.

Foederati

Outside the regular army were substantial numbers of allied forces, generally known as foederati (from foedus = "treaty") or symmachi in the East. The latter were forces supplied either by barbarian chiefs under their treaty of alliance with Rome or dediticii. Such forces were employed by the Romans throughout imperial history: the battle scenes from Trajan's Column in Rome show that foederati troops played an important part in the Dacian Wars (101–6).

In times when they were needed, or on a regular basis, the ally would supply troops to support Roman operations. Normally their service would be limited to the region where the tribe lived, but sometimes could be deployed elsewhere. In the 4th century, these forces were organised into units based on a single ethnic group loosely called numeri ("troops", although numerus was also the name of a regular infantry unit). They served alongside the regular army for the duration of particular campaigns or for a specified period. They were commanded by their own leaders. It is unclear whether they used their own weapons and armour or the standard equipment of the Roman army. The more useful and long-serving numeri appear to have been absorbed into the regular late army, rapidly becoming indistinguishable from other units. There is no evidence of irregular barbarian units becoming part of the regular Principate army until the 3rd century.

Ranks, pay and benefits

Common soldiers

At the bottom end of the rank pyramid were the common soldiers: pedes (infantryman) and eques (cavalryman). The 4th century soldier's remuneration consisted of (a) an annual cash salary (stipendium); (b) food rations (annona), which were paid in kind or in cash equivalent, always the latter from the late 4th century (in addition cavalrymen received a fodder allowance (capitus) probably worth the same as the annona; (c) an equipment allowance to cover clothes and maybe armour and weapons; (d) occasional cash bonuses (donativa) and (e) a discharge bonus (praemium). The annona and equipment allowance were obviously not disposable, as they were needed for subsistence. The stipendium was in Diocletian's time ca. 1,800 denarii, then officially worth 2 gold solidi, but actually worth much less due to debasement of the coin's silver content. By the time of Constantine, it was virtually worthless and ceased being paid regularly in mid 4th century.

The soldier's sole substantial disposable income came from the donativa, as these were paid in solidi (which were never debased), or in pure silver. There was a regular donative of 5 solidi every five years of an Augustus reign (i.e. one solidus p.a.) Also, on the accession of a new Augustus, 5 solidi plus a pound of silver (worth 4 solidi) were paid. The 12 Augusti that ruled the West between 284 and 395 averaged about nine years per reign. Thus the accession donatives would have averaged about 1 solidus p.a. It is also possible that this bonus was paid for each Augustus and/or each Caesar. The late soldier's disposable income would thus have averaged around 2–4 solidi per annum. Even at the high end of the range, this was far less than for an early Principate soldier. An auxiliary of the latter period had disposable income (after food and equipment deductions) of 140 Principate denarii, equivalent to ca. 8 solidi p.a. (assuming he was not also paid donativa). A Principate legionary, who certainly received donativa, enjoyed about 12 solidi p.a. of disposable income. The late soldier's discharge bonus was also minuscule compared with a 2nd century legionary's. The latter received 3,000 Principate denarii, equivalent of 180 solidi, a very large sum representing about 10 years' gross salary. His late counterpart received a retirement package (including a plot of land) worth just a tenth of the legionary's. Template:FixHTML

Roman infantryman in the time of Diocletian (r.284–305). Unlike the 1st/2nd century standard "Imperial Gallic" helmet, this late helmet has a nose-guard and its hinged cheek-guards cover the ears. This afforded better facial and head protection, but at the cost of reduced field of vision and hearing. The armour is chain mail (lorica hamata) and the shield oval/round, the typical armour of the 2nd century auxilia.

4th century foot soldier. Note the differences with 2nd century attire: trousers instead of bare legs; boots instead of sandals. The tunic has long sleeves, unlike the short-sleeved tunic of the Principate. This soldier is armed with a single heavy thrusting-spear

4th century soldier wearing leather cuirass arguing with a tubicen (trumpeter) wearing a Pannonian cap, a typical military uniform headdress of the era. Note that both soldiers are armed with a spatha (a longer sword used only by the cavalry during the Principate) instead of the gladius, the short sword that was the standard infantry weapon until the 3rd century. The sword is now worn on the left side, rather than the right as previously, probably to facilitate (un)sheathing of the longer sword by a right-handed soldier

6th century parade helmet from the Sutton Hoo royal burial site. Based on a late Roman design, this type of helmet was commonly used by the Roman cavalry of the 4th-6th centuries. Note the face-guard and deep, hinged neck-guard. British Museum, London

Bas-relief of a Parthian heavily armoured mounted warrior. He is wearing what is probably a chain-mail face-guard. This is possibly the kind of armour denoted by the Roman term clibanarius, probably meaning "furnace man" in reference to the heat that would build up inside such all-encompassing armour. Note the armoured caparison for the horse. From Taq-e Bostan, Iran

External images
Roman cataphract cavalryman
Reenactor as Roman cataphract
Reenactor as Late Roman staff slinger
Reenactor as Late Roman archer
Reenactor as Late Roman skirmisher with javelins

Template:FixHTML Retired veterans were granted important tax privileges, as they were in the 2nd century. In the Principate, auxiliary veterans were granted Roman citizenship, which carried exemption from direct taxes (tributum): poll tax (tributum capitis) and other imposts. With the grant of Roman citizenship to all the free inhabitants of the empire in 212, citizens' exemption from tributum was abolished. But it was retained for military veterans. In the 4th century, veterans were exempt from poll tax, customs and market dues. They were also exempt from corvées (compulsory labour for the state). Finally, if they owned land, they were not subject to curial duties (i.e. service in the town councils, which was extremely unpopular, as it was unpaid and indeed expensive, as curiales were expected to pay for public works and events out of their own pockets).

Despite the disparity with the Principate, Jones and Elton argue that 4th century remuneration was attractive compared to the hard reality of existence at subsistence level that most recruits' peasant families had to endure. Against that has to be set the clear unpopularity of military service.

However, pay would have been more attractive in higher-grade units. As in the Principate army, pay levels varied according to the unit's position in the military hierarchy. In the Principate, pay levels were (in descending order) Praetorian Guard, legions, auxilia, with cavalry paid 20–40% more than infantry in each corps. In the late army, the top of the pay pyramid were the scholae elite cavalry regiments. Next came palatini units, then comitatenses, and finally limitanei. There is little evidence about the pay differentials between grades. But life for a scholaris (schola cavalryman), for example, would have been very comfortable. An actuarius (quartermaster) of a comitatus regiment was paid 50% more than his counterpart in a pseudocomitatensis regiment.

Junior officers

Junior officer grades in old-style units (legiones, alae and cohortes) remained the same as under the Principate up to and including centurion and decurion. In the new-style units, (vexillationes, auxilia, etc), ranks with quite different names are attested. So little is known about these ranks that it is impossible to equate them with the traditional ranks with any certainty. Vegetius states that the ducenarius commanded, as the name implies, 200 men. If so, the centenarius may be the equivalent of a centurion in the old-style units. Probably the most accurate comparison is by pay levels:

RANKS IN THE 4th CENTURY ARMY

Multiple of basic pay (2nd c.) or annona (4th c.)	2nd c. cohors (ascending ranks)	2nd c. ala (ascending ranks)	XXX	New-style units (ascending ranks)
1	pedes	gregalis		pedes (eques)
1.5	tesserarius	sesquiplicarius		semissalis
2	signifer optio vexillarius	signifer curator? vexillarius		circitor biarchus
2.5 to 5	centurio centurio princeps beneficiarius?	decurio decurio princeps beneficiarius?		centenarius (2.5) ducenarius (3.5) senator (4) primicerius (5)

NOTE: Ranks correspond only in pay scale, not necessarily in function

Senior officers

SENIOR RANKS IN THE 4TH CENTURY ARMY

Pay scale (multiple of pedes)	Rank (ascending order)	Job description
12	Protector	officer cadet
n.a.	Tribunus	regimental commander
n.a.	Comes (junior)	brigade commander
100	Dux	border army commander
n.a.	Comes (rei militaris)	commander, smaller regional comitatus
n.a.	Vicarius	deputy to magister militum
n.a.	Magister militum	commander, comitatus praesentalis or larger regional comitatus

A significant innovation of the 4th century was the corps of protectores. Officers given a commission by the emperor initially held the rank of protector. Although protectores were supposed to be soldiers who had risen through the ranks by meritorious service, it became a widespread practice to admit to the corps young men from outside the army (often the sons of senior officers). The protectores formed a corps that was both an officer training school and pool of staff officers available to carry out special tasks for the magistri militum and the emperor (as protectores domestici). For example, protectores might be detailed to supervise recruitment for the army; carry out inspections of goods on public highways; arrest important persons; or supervise fortification works. The protectores domestici were organised in four scholae under a comes domesticorum. After a few years' service in the corps, a protector would normally be promoted to command a military regiment.

Regimental commanders were known by one of three possible titles: tribunus, praefectus or praepositus. Tribunus was the most common title and was often used loosely to mean the commander of any unit. Strictly speaking, the commanders of scholae, vexillationes, auxilia, legiones palatinae and cohortes were called tribuni. In the Principate, only a minority of unit commanders were known as tribuni militum (mostly the commanders of milliary auxiliary regiments), with most tribuni serving as staff officers in the legions. The common use of the title in the later era lends support to the hypothesis that legions were split up during the third century to form smaller units.

Equipment

The basic equipment of a 4th century foot soldier was essentially the same as in the 2nd century: metal armour cuirass, metal helmet, shield, sword, dagger. Some evolution took place during the 3rd century. Trends included the adoption of warmer clothing; the disappearance of distinctive legionary armour and weapons; the adoption by the infantry of equipment used by the cavalry in the earlier period; and the greater use of heavily armoured cavalry called cataphracts.

Clothing

In the 1st and 2nd centuries, a Roman soldier's clothes consisted of a single-piece, short-sleeved tunic whose hem reached the knees and special hobnailed sandals (caligae). This attire, which left the arms and legs bare, had evolved in a Mediterranean climate and was not suitable for northern Europe in cold weather. In those climes, long-sleeved tunics, trousers (bracae), socks (worn inside the caligae) and laced boots were commonly worn in winter by the late 1st century. During the 3rd century, these items of clothing became much more widespread.

Armour

Legionary soldiers of the 1st and 2nd centuries had exclusive use of the lorica segmentata or laminated-strip cuirass which was a complex piece of armour which provided superior protection to the other types of Roman armour, chain mail (lorica hamata) and scale armour (lorica squamata). Testing of modern replicas have demonstrated that this kind of armour was impenetrable to most direct and missile strikes. It was, however, uncomfortable: reenactors have discovered that chafing renders it painful to wear for longer than a few hours at a time. It was also expensive to produce and difficult to maintain. In the 3rd century, the segmentata appears to have been dropped and troops are depicted wearing chain mail (mainly) or scales, the standard armour of the 2nd century auxilia. The arechaeological record shows that most late soldiers wore metal armour, despite Vegetius' statement to the contrary. Officers generally seem to have worn simple bronze or iron cuirasses, as in the days of the Republic.

In the 1st and 2nd centuries, the standard design of the Roman infantry helmet is today called the "Imperial Gallic" type. Its essential features were a single-piece bowl with reinforced front to resist downward sword-thrusts, a wide neck-guard at a shallow angle and large, hinged cheek-guards. However, the front of the face and ears were left uncovered, to allow maximum field of vision and range of hearing. This inevitably entailed frequent facial injuries. The cavalry version of the Imperial Gallic differed in having extended cheek-guards that covered the ears and neck-guards that were much longer and more steeply-angled but also narrower than the infantry helmet. This afforded more protection to the rear and sides of the head, which were more likely to receive blows in cavalry mêlées than in an infantry line, but at the expense of poorer vision and hearing. During the 3rd century, infantry helmets adopted some of these cavalry features. In some cases extra protective features were added, such as nose-guards, although the latter were by no means universal, as the reliefs on the Arch of Constantine show. Face-guards of mail or metal piece with eye-holes were also added occasionally, especially to cavalry helmets. Later helmets were predominantly of the "Intercisa" design: the bowl was made of two separate pieces joined by a riveted ridge in the middle. This was simpler and cheaper to manufacture than the earlier single-bowl type, but structurally weaker and therefore offered less effective protection.

The late Roman army contained a significant number of heavily armoured cavalry called cataphracti (from the Greek kataphraktos, meaning "covered all over"). These were covered from neck to foot by scale and/or lamellar, and their horses were often armoured also. Cataphracts carried a long, heavy lance called a contus, ca. 3.65 m long, that was held in both hands. Some also carried bows. The central tactic of cataphracts was the shock charge, which aimed to break the enemy line by concentrating overwhelming force on a defined section of it. A type of cataphract called a clibanarius also appears in the 4th century record. This term may de derived from Greek klibanos (a bread oven) or from a Persian word. It is likely that clibanarius is simply an alternative term to cataphract, or it may have been a special type of cataphract. It is possible that the term, which may refer to the build-up of heat in enclosed armour, refers to the use of a fully-enclosed helmet (similar to a medieval great helm) with slit-opening for the eyes.

This type of cavalry had been developed by the Iranic horse-based nomadic tribes of the Eurasian steppes from the 6th-century BCE onwards: the Scythians and their kinsmen the Sarmatians. The type was adopted by the Parthians in the 1st century BCE and later by the Romans, who needed it to counter Parthians in the East and the Sarmatians along the Danube. The first regiment of Roman cataphracts to appear in the archaeological record is the ala I Gallorum et Pannoniorum cataphractaria, attested in Pannonia in the early 2nd century. Although Roman cataphracts were not new, they were far more numerous in the late army, with most regiments stationed in the East.

The legionary scutum, a convex rectangular shield renowned for allowing troops to lock shields protectively in battle, such as the testudo formation, also disappeared during the 3rd century. All troops adopted the auxiliary oval (or sometimes round) shield (clipeus).

Hand weapons

The gladius, a short (median length: 460 mm) stabbing-sword that was designed for close-quarters fighting, and was standard for the Principate infantry (both legionary and auxiliary), also was phased out during the 3rd century. The infantry adopted the spatha, a longer (median length: 760mm) sword that during the earlier centuries was used by the cavalry only. At the same time, infantry acquired a heavy thrusting-spear (hasta) which became the main close order combat weapon to replace the gladius, as the spatha was too long to be swung comfortably in tight formation (although it could be used to stab). The infantry's adoption of the thrusting-spear as the main melee weapon, combined with enhanced missile capability, shows a greater emphasis on fighting the enemy "at arm's length".

Missiles

In addition to his thrusting-spear, a late foot soldier might also carry a throwing-spear (verrutum) or a spiculum, a kind of heavy, long pilum, similar to an angon. Alternatively, a couple of short javelins (lanceae). Late infantrymen often carried half a dozen lead-weighted throwing-darts called plumbatae (from plumbum = "lead"), with an effective range of ca. 30 m, well beyond that of a javelin. The darts were carried clipped to the back of the shield. The late foot soldier thus had greater missile capability than his Principate predecessor, who was usually limited to just one pilum. Late archers continued to use the recurved composite bow as their standard. This was a sophisticated, compact and powerful weapon, suitable for mounted and foot archers alike (the cavalry version being more compact than the infantry's). A small number of archers may have been armed with crossbows (manuballistae).

Fortifications

The Walls of Theodosius II at Constantinople, built 408–413. Note the massive crenellated towers and surviving sections of wall. The walls actually consisted of a triple curtain, each one overlooking the other. They proved impregnable to even the largest armies until the introduction of explosive artillery in the later Middle Ages

Aerial view of Colonia Agrippina (Cologne, Germany) in the Roman era. Note (bottom right) the Constantinian fortress of Divitia (Deutz), on the opposite bank of the Rhine. Its main function was to guard the approach to the newly-built bridge (310) and to act as a base protect fluvial traffic. Several such cross-river forts were built along the Rhine-Danube frontier in the late period

Compared to the 1st and 2nd centuries, the 3rd and 4th centuries saw much greater fortification activity, with many new forts built. Later Roman fortifications, both new and upgraded old ones, contained much stronger defensive features than their earlier counterparts. In addition, the late 3rd/4th centuries saw the fortification of many towns and cities including the City of Rome itself and its eastern sister, Constantinople.

Roman forts of the 1st/2nd centuries, whether castra legionaria (inaccurately translated as legionary "fortresses") or auxiliary forts, were clearly residential bases that were not designed to withstand major assault. The typical rectangular "playing-card" shape, the long, thin and low walls and shallow ditch and the unfortified gates were not easily defensible features and their purpose was delimitation and keeping out individual intruders.

In contrast, later forts were built to much higher defensive specifications, including the following features:

1. Deeper (average: 3 m) and much wider (av. 10 m) perimeter ditches (fossae). These would have flat floors rather than the traditional V-shape. Such ditches would make it difficult to bring siege equipment (ladders, rams, and other engines) to the walls. It would also concentrate attackers in an enclosed area where they would be exposed to missile fire from the walls.
2. Higher (av. 9 m) and thicker (av. 3 m) walls. Walls were made of stone or stone facing with rubble core. The greater thickness would protect the wall from enemy mining. The height of the walls would force attackers to use scaling-ladders. The parapet of the rampart would have crenellations to provide protection from missiles for defenders.
3. Higher (av. 17.5 m) and projecting corner and interval towers. These would enable enfilading fire on attackers. Towers were normally round or half-round, and only rarely square as the latter were less defensible. Towers would be normally be spaced at 30 m intervals on circuit walls.
4. Gate towers, one on each side of the gate and projecting out from the gate to allow defenders to shoot into the area in front of the entrance. The gates themselves were normally wooden with metal covering plates to prevent destruction by fire. Some gates had portcullises. Postern gates were built into towers or near them to allow sorties.

More numerous than new-build forts were old forts upgraded to higher defensive specifications. Thus the two parallel ditches common around earlier forts could be joined by excavating the ground between them. Projecting towers were added. Gates were either rebuilt with projecting towers or sealed off by constructing a large rectangular bastion. The walls were strengthened by doubling the old thickness. Upgraded forts were generally much larger than new-build. New forts were rarely over one hectare in size and were normally placed to fill gaps between old forts and towns. However, not all of the old forts that continued to be used in the 4th century were upgraded e.g. the forts on Hadrian's Wall and some other forts in Britannia were not significantly modified.

The main features of late Roman fortification clearly presage those of medieval castles. But the defensibility of late Roman forts must not be exaggerated. Late Roman forts were not always located on defensible sites, such as hilltops and they were not designed as independent logistic facilities where the garrison could survive on internal supplies (water in cisterns or from wells and stored food) for months or even years. They remained bases for troops that would sally out and engage the enemy in the field.

Nevertheless, the benefits of more defensible forts are evident: they could act as temporary refuges for overwhelmed local troops during barbarian incursions, while they waited for reinforcements. The forts were difficult for the barbarians to take by assault, as they generally lacked the necessary equipment. The forts could store sufficient supplies to enable the defenders to hold out for a few days, and to supply relieving troops. They could also act as bases from which defenders could make sorties against isolated groups of barbarians and to cooperate with relieving forces.

The question arises as to why the 4th century army needed forts with such defensive features that the 2nd century army apparently did not. E. Luttwak argues that defensible forts were an integral feature of a 4th century defence-in-depth "grand strategy", while in the 2nd century "preclusive defence" rendered such forts unnecessary . But the existence of such a "strategy" is strongly disputed by several scholars, as many elements of the late Roman army's posture were consistent with continued forward defence. An alternative explanation is that preclusive defence was still in effect but was not working as well as previously and barbarian raids were penetrating the empire more frequently.(see Strategy, below)

Strategy and tactics

Strategy

Edward Luttwak's Grand Strategy of the Roman Empire (1976) launched the thesis that in the 3rd and early 4th centuries, the empire's defence strategy mutated from "forward defence" (or "preclusive defence") in the Principate to "defence-in-depth" in the 4th century. This section contains a brief summary of the debate on this issue. Readers seeking a more detailed analysis should consult Defence-in-depth (Roman military).

According to Luttwak, the Principate army had relied on neutralising imminent barbarian incursions before they reached the imperial borders. This was achieved by stationing units (both legions and auxiliary regiments) right on the border and establishing and garrisoning strategic salients beyond the borders. The response to any threat would thus be a pincer movement into barbarian territory: large infantry and cavalry forces from the border bases would immediately cross the border to intercept the coalescing enemy army.

According to Luttwak, the forward defence system was always vulnerable to unusually large barbarian concentrations of forces, as the Roman army was too thinly spread along the enormous borders to deal with such threats. In addition, the lack of any reserves to the rear of the border entailed that a barbarian force that successfully penetrated the perimeter defences would have unchallenged ability to rampage deep into the empire before Roman reinforcements from other border garrisons could arrive to intercept them.

The essential feature of defence-in-depth, according to Luttwak, was an acceptance that the Roman frontier provinces themselves would become the main combat zone in operations against barbarian threats, rather than the barbarian lands across the border. Under this strategy, border forces would not attempt to repel a large incursion. Instead, they would retreat into fortified strongholds and wait for mobile forces (comitatenses) to arrive and intercept the invaders. Border forces would be substantially weaker than under forward defence, but their reduction in numbers (and quality) would be compensated by the establishment of much stronger fortifications to protect themselves.

But the validity of Luttwak's thesis has been strongly disputed by a number of scholars, especially in a powerful critique by B. Isaac, the author of the fundamental study of the Roman army in the East (1992). Isaac claims that the empire did not have the intelligence capacity or centralised military planning to sustain a grand strategy e.g. there was no equivalent to a modern army's general staff. In any case, claims Isaac, the empire was not interested in "defence" at all: it was fundamentally aggressive both in ideology and military posture, up to and including the 4th century.

Furthermore, there is a lack of substantial archaeological or literary evidence to support the defence-in-depth theory. (a) J.C. Mann points out that there is no evidence, either in the Notitia Dignitatum or in the archaeological record, that units along the Rhine or Danube were stationed in the border hinterlands. On the contrary, virtually all forts identified as built or occupied in the 4th century on the Danube lay on, very near or even beyond the river, strikingly similar to the 2nd century distribution.

Another supposed element of "defence-in-depth" were the comitatus praesentales (imperial escort armies) stationed in the interior of the empire. But Luttwak himself admits that these were too distant from the frontier to be of much value in intercepting barbarian incursions. Their arrival in theatre could take weeks, if not months. Although they are often described as "mobile field armies", in this context "immobile" would be a more accurate description. Luttwak terminates his analysis at the end of Constantine's reign, before the establishment of the regional comitatus. Unlike the imperial escort armies, these were close enough to the theatre of operations to succour the border troops. But their stationing may have differed little from the location of legions in the 2nd century, even though they apparently wintered inside cities, rather than in purpose-built legionary bases. For example, the two comitatus of Illyricum (East and West) are documented as wintering in Sirmium, which was a major legionary base in the Principate.

Furthermore, the late empire maintained a central feature of Principate forward defence: a system of treaties of mutual assistance with tribes living on the imperial frontiers. The Romans would promise to defend the ally from attack by its neighbours. In return, the ally would promise to refrain from raiding imperial territory, and prevent neighbouring tribes from doing the same. Although the allies would officially be denoted tributarii (i.e. subject to paying tribute to Rome, in cash or in kind), in practice the loyalty of the ally was often secured by gifts or regular subsidies from Rome. This practice was applied on all the frontiers. The Romans continued to assist the client tribes to defend themselves in the 4th century. For example, Constantine I's army constructed two massive lines of defensive earthworks, 100–250 km beyond the Danube, totalling ca. 1,500 km in length, the Devil's Dykes in Hungary/Romania and the Brazda lui Novac de Nord in Romania. Their purpose was to protect Dacian and Sarmatian tributary tribes of the Tisza and Wallachian plains against Gothic incursions. This created a Transdanubian buffer zone, extending from Aquincum (Budapest) all the way to the Danube delta, obviously contradicting the proposition that the empire's Danubian border provinces were themselves envisaged as buffer zones.

Late Roman emperors continued major and frequent offensive operations beyond the imperial borders throughout the 4th century. These were strikingly similar to the pincer movements described by Luttwak as being characteristic of forward defence in the early Principate. For example, Valentinian I's campaign against the Quadi in 375. Julian in 356–60 and Valentinian I in 364–9 carried out annual operations across the Rhine designed to force the submission of local tribes and their acceptance of tributarii status.

The late army's "defence" posture thus contains many elements that are similar to the Principate army's, raising the question of whether defence-in-depth was ever in reality contemplated (or implemented) as a strategy. But the debate about defence-in-depth is still very much alive in academic circles.

Role of cavalry

A traditional thesis is that cavalry assumed a much greater importance in the 4th century army than it enjoyed in the 2nd century. According to this view, cavalry increased significantly as a proportion of the total forces and took over the leading tactical role from the infantry. It also enjoyed much higher status than in the 2nd century. At the same time, the infantry declined in efficiency and value in operations, leaving the cavalry as the effective arm. In fact, there is no good evidence to support this view, and plenty of evidence against it.

As regards numbers, the 2nd century army had ca. 80,000 cavalry out of ca. 385,000 total effectives i.e. cavalry constituted ca. 21% of the total forces. Estimating the cavalry share in the 4th century army is impeded by the fundamental problem that unit sizes are not known with any certainty. About one third of the army units in the Notitia are cavalry, but cavalry numbers were less than that proportion of the total because cavalry unit sizes were smaller. The available evidence suggests that the proportion of cavalry was much the same as in the 2nd century: in 478, a comitatus of 38,000 men contained 8,000 cavalry (21%).

There is thus no evidence for an increase in the relative importance of cavalry in the army. It appears that in the 4th century there was a substantial increase in the number of heavily-armoured cavalry in the East (cataphracti and clibanarii). It is important, however, not to exaggerate the role of cataphracts: only 15% of comitatenses cavalry units were cataphracts.

The supposed higher status of cavalry in the 4th century is also open to doubt. This view is largely based on underestimating the importance of cavalry in the 2nd century. Cavalry always had greater prestige than infantry in the Principate: in the time of Domitian (r. 81–96), although an auxiliary infantryman (pedes cohortalis) was paid less than a legionary foot soldier, a cavalryman from a cohors equitata (eques cohortalis) was paid the same, and an elite ala cavalryman (eques alaris) 20% more.

The view of some modern scholars that the 4th century cavalry was a more efficient service than the infantry was certainly not shared by Ammianus and his contemporaries. Ammianus describes three major battles which were actually or nearly lost due to the incompetence or cowardice of the Roman cavalry. (1) The Battle of Strasbourg (357), where the cavalry, including cataphracts, were routed by their German counterparts at an early stage, leaving the Roman infantry right wing dangerously exposed. After fleeing behind the infantry lines, it took the personal intervention of Julian to rally them and persuade them to return to the fight. (The cataphracts were later ordered to wear female clothes by Julian as punishment). (2) During his Persian campaign (363), Julian was obliged to sanction two cavalry units for fleeing when caught by surprise attacks (one unit was decimated, the other dismounted). Later, the Tertiaci cavalry regiment was ordered to march with the camp followers for deserting the field just as the infantry was on the point of breaking the Persian line. (3) At the Battle of Adrianople (378), the Roman cavalry was largely responsible for the catastrophic defeat. Scholae units started the battle by an unauthorised attack on the enemy wagon circle, at a moment when their emperor Valens was still trying to negotiate a truce with the Goths. The attack failed, and when the Gothic cavalry appeared, the Roman cavalry fled, leaving the Roman infantry left wing exposed. The Gothic cavalry then routed the Roman left wing, and the battle was as good as lost.

Role of infantry

The idea that in the 4th century, cavalry was the main tactical arm, with an ineffectual infantry relegated to a subsidiary role, is also false. The table above shows that the field armies continued to be dominated by infantry. The latter included large numbers of crack infantry regiments with an awesome reputation, including the famed Batavi, still classified as elite after 400 years of service to the empire. The auxilia palatina were rated among the best regiments in the army.

Coin showing (obverse) head of emperor Julian (ruled 361–3) with diadem and (reverse) soldier bearing standard holding kneeling captive by the hair and legend VIRTVS EXERCITVS ROMANORVM ("Courage of the Roman army"). Gold solidus. Sirmium mint

Most battles fought by Roman forces in the 4th century continued to be essentially infantry encounters with cavalry playing a supporting role. A good illustration of the combat tactics of a 4th century field army is the Battle of Strasbourg in 357, described by Ammianus in a somewhat fragmentary account. The Caesar (deputy emperor) Julian, in command of the comitatus Galliarum (field army of Gaul) of 13,000 men confronted a major raiding force of Alamanni Germans which outnumbered the Romans by 3 to 1. Julian's force was seriously understrength (due to losses in previous campaigns against the Germans) but high-quality, including elite infantry regiments of Batavi, Cornuti, Bracchiati Primani and Regii. The encounter took place on a rise a few miles from the river Rhine near Argentorate (Strasbourg).

The battle started disastrously for the Romans, with their cavalry, largely made up of cataphracti, routed by the German cavalry. But the infantry showed remarkable skill, discipline and resilience throughout, saving the day at two critical moments. The first was after the flight of the Roman cavalry, when the Roman frontline's right wing was exposed to joint attack by the German cavalry and infantry. The Bracchiati and Cornuti regiments on the wing managed to hold formation until the regrouped Roman cavalry returned to the fray. The second critical moment was after the German spearhead succeeded in breaking through the centre of the Roman frontline. Despite being split in two, the regiments of the Roman frontline managed to hold formation until the regiments of the rear line could move up to plug the gap in the frontline (see Battle of Strasbourg for a detailed account).

The excellent performance of the infantry, both comitatenses and limitanei, is a striking feature of Ammianus' history, in contrast to the often lamentable failure of the officially senior cavalry service. At the Persian siege of Amida, Ammianus' eye-witness account describes the city's defence by limitanei units as skilful and tenacious, if ultimately unsuccessful. Even at the disaster of Adrianople, the Roman infantry fought heroically, despite being abandoned by their cavalry and surrounded on three sides by overwhelmingly superior numbers of Goths.

The "barbarisation" theory

Drawing of Flavius Stilicho, the barbarian-born general who was magister utriusque militiae (commander-in-chief) of West Roman forces 395–408. The general is depicted in the standard attire of a common foot soldier of the time. He was made a scapegoat for the barbarian invasions of 405–6, although in reality his military skill may have saved the West from early collapse. Derived (1848) from an ivory diptych at Monza, Italy

For the late Roman army, a common hypothesis has become established that the much greater number of barbarian recruits to the Roman army resulted in the decline of its discipline, reliability and effectiveness and was a major factor in the collapse of the western Roman empire. This view ultimately derives from Edward Gibbon's 18th-century magnum opus, The Decline and Fall of the Roman Empire. This hypothesis is known as the barbarisation theory.

According to this view, the barbarian officers and men recruited by the late army, coming from tribes that were traditional enemies of Rome, had no real loyalty to Rome and often betrayed her interests, colluding with invading barbarian tribes, especially if those tribes were their own. At the same time, the spread of barbarian customs and culture military led to a decline in traditional discipline, and internal army disunity due to friction between Romans and barbarians. Ultimately, the army degenerated into just a collection of foreign mercenary bands that were incapable of defending the empire effectively.

But there is little evidence to support this view and compelling reasons to reject it. Firstly, the late army was clearly not ineffective. The Eastern empire did not collapse, even though its army contained at least the same proportion of barbarians as the West, if not greater. An analysis of the ethnicity of Roman army officers named in the sources shows that in the period 350–99, barbarians constituted 23% of the whole army. The same figure for period 449–76 officers, virtually all Easterners (as the Western army had dissolved) was 31%. In the Notitia, 55 Eastern regiments carry barbarian names, compared with 25 in the Western army. The regular army in the West remained an effective and formidable force until the disintegration of the West in the period after 406. It continued to win most of its encounters with barbarian forces e.g. the defeat of Radagaisus in 405.

Most damningly for barbarisation, barbarian-born troops appear to have been especially concentrated in the elite vexillationes and auxilia units of the comitatus: in the elite auxilia palatina infantry regiments, the proportion of barbarians in the ranks appears to number anywhere between a third and a half of effectives. This implies that they were considered highly reliable, as well as of first-rate combat capability. Ammianus himself never chracterises barbarian-born troops as unreliable. On the contrary, his evidence is that barbarian soldiers were as loyal, and fought as hard, as Roman ones.

Incidents of alleged barbarian treachery in the regular army are very few (three in all) and isolated. They all involved officers who allegedly warned their own tribal groups of campaigns planned against them. Only one case is clearcut or certain. There is a tendency by some modern scholars to ascribe a degree of nationalist sentiment to ancient barbarians that did not exist. For example, German tribes were constantly fighting each other and even within such tribal confederations as the Franks or Alamans there was bitter feuds between the constituent tribes and clans. Conflicts of loyalty could only arise when the Roman army was campaigning against a barbarian's own specific clan. It is also a fact that most barbarian-born troops became assimilated into Roman culture. There is no known case of a barbarian-born soldier returning to his homeland after completing his service (although deserters often did).

The performance of barbarian senior officers was no worse than that of their Roman counterparts. It is true that some barbarian magistri militum could be treacherous. A good example is Ricimer: it is likely that he colluded with the Vandals in Africa to defeat two Roman expeditions against them. This was disastrous for the Western empire, which needed African grain revenue to pay for its army. But Roman-born generals could be equally disloyal e.g. Flavius Aetius, who used his contacts with the Huns to lead a Hunnic army into Italy in support of the usurper Joannes in 425. Indeed a key reason for the dominance of barbarian-born army leaders in the West in the period 395–476 is the fact that non-Romans could not aspire to become emperor themselves and were thus considered less likely to rebel against the child-emperors Honorius (ruled 393–423, acceeded at age 9) and Valentinian III (r. 425–55, acc. age 6) than Roman-born generals. Rebellions by barbarian-born generals were greatly outnumbered by Roman usurpation attempts.

After the Adrianople disaster in 378, entire sub-tribes of barbarians entered the empire with or without the Roman government's permission and proved impossible to expel. These were generally bound by treaty to provide troops for the Roman army in return for permission to settle certain regions. They were thus known as foederati even though they were quite different from the allied contingents that the empire had employed for centuries. These were certainly highly destructive, as demonstrated by the career of the Gothic leader Alaric, who sacked Rome in 410. But they were not part of the regular army and thus were irrelevant to its performance. In any case, even these were not only liabilities for the Romans. Alaric himself and his men fought hard for Rome for several years before rebelling. Aetius was largely dependent on his Alanic allies for his success in maintaining Roman control over Gaul for almost 30 years (425–53).

In conclusion, the barbarisation theory appears to lack any evidential basis as regards the regular Roman army of the 4th century. On the contrary, it is likely that barbarian recruitment was crucial to the army's continued existence, by providing a badly-needed source of first-rate recruits.

References

Ancient

• Ammianus Marcellinus, Roman History (late 4th c.)
• Zosimus, Historia Nova (5th century)
• Notitia Dignitatum, Augustana (late 4th/early 5th c.)

Modern

• Duncan-Jones, Richard (1990). Structure and Scale in the Roman Economy.
• Duncan-Jones, Richard (1994). Money and Government in the Roman Empire.
• Elton, Hugh (1996). Warfare in Roman Europe, AD 350–425. Oxford University Press. ISBN 978-0198152415.
• Goldsworthy, Adrian (2000). Roman Warfare.
• Goldsworthy, Adrian (2003). Complete Roman Army.
• Hassall, Mark (2000). "The Army" in Cambridge Ancient History 2nd Ed Vol XI (The High Empire 70–192).
• Heather, Peter (2005). Fall of the Roman Empire.
• Holder, Paul (2003). Auxiliary Deployment in the Reign of Hadrian.
• Isaac, B. (1992). Limits of Empire.
• Jones, A.H.M. (1964). Later Roman Empire.
• Lee, A.D. (1997). "The Army" in Cambridge Ancient History 2nd Ed Vol XIII (The Later Empire 337–425).
• Luttwak, Edward (1976). Grand Strategy of the Roman Empire.
• Mattingly, David (2006). An Imperial Possession: Britain in the Roman Empire.
• Tomlin, R. S. O. (1988). "The Army of the Late Empire" in The Roman World (ed J. Wacher).

See also

• Roman auxiliaries
• East Roman army
• Structural history of the Roman military
• Battle of Strasbourg

External links

• Late Roman army reenactors