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Great Conspiracy

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The Great Conspiracy
Part of the Roman occupation of Britain

Northern Roman Britain, c. 350–400 AD.
Result Roman victory
Roman Empire Picts
Roman deserters
rebellious Britons
Commanders and leaders
Count Theodosius
Valentinus and others

The Great Conspiracy was a year-long state of war and disorder that occurred near the end of Roman Britain. The historian Ammianus Marcellinus described it as a barbarica conspiratio, which took advantage of a depleted military force in the province; many soldiers had marched with Magnentius in his unsuccessful bid to become emperor. Few returned, and supply, pay, and discipline in the following years may have been deficient.

It is difficult to ascertain the exact chronology of the events because their main source, Ammianus, was living in Antioch at that time. His information looks second-hand and confused and some is inconsistent with that produced by other sources.[1]


According to Ammianus, the following events occurred: In the winter of 367, the Roman garrison on Hadrian's Wall rebelled and allowed Picts from Caledonia to enter Britannia. Simultaneously, Attacotti, the Scotti from Hibernia and Saxons from Germania landed in what might have been coordinated and pre-arranged waves on the island's mid-western and southeastern borders, respectively.[citation needed] The warbands managed to overwhelm nearly all of the loyal Roman outposts and settlements. The entire western and northern areas of Britannia were overwhelmed; the cities sacked; and the civilian Romano-British murdered, raped, or enslaved. Franks and Saxons also landed in northern Gaul.

Nectaridus, the comes maritime tractus (commanding general of the sea coast region), was killed, and a Dux, Fullofaudes, was either besieged or captured. The location of their defeats are often supposed to have been in Britain, but may have been in Gaul.[2] The remaining loyal army units stayed garrisoned inside southeastern cities.[3]

The miles areani, the local Roman agents who provided intelligence on barbarian movements, seem to have betrayed their paymasters for bribes, which made the attacks completely unexpected. Deserting soldiers and escaped slaves roamed the countryside and turned to robbery to support themselves. Although the chaos was widespread and initially concerted, the rebels had aims simply of personal enrichment and worked as small bands rather than larger armies.

Roman response[edit]

Early attempts[edit]

Emperor Valentinian I was campaigning against the Alamanni at the time and so was unable to respond personally. A series of commanders to act in his stead were chosen but swiftly recalled.

The first was Severus, the emperor's comes domesticorum, who was soon recalled and replaced by Jovinus, the magister equitum.[3] Jovinus then wrote back to Valentinian requesting reinforcements. The Emperor recalled Jovinus, probably to take part in a campaign along the Rhine, which was a higher priority, and then sent out Flavius Theodosius.[4] It has been supposed that Severus and Jovinus travelled to Britain to make their findings and back to the Emperor to report, but Ammianus does not state this and the known chronology of Valentinian's movements at the time (recorded by edicts in the Codex Theodosianus) would make it difficult for them to do so before the summer was over. They may only have traveled to areas that barbarians had attacked in Northern Gaul.[5]

Arrival of Theodosius[edit]

In the spring of 368, a relief force, commanded by Flavius Theodosius, gathered at Bononia (Boulogne-sur-Mer). It included four units, Batavi, Heruli, Iovii and Victores, as well as his son, the later Emperor Theodosius I, and probably the later usurper Magnus Maximus, his nephew.

Theodosius took advantage of a break in the winter weather to cross the Channel to Richborough, which left the rest of his troops at Bononia to await better weather. That enabled Theodosius to gather vital intelligence.[6] He discovered that the British troops had been overwhelmed, refused to fight, or deserted, and many may not have been paid.[7]

Once the troops had landed, Theodosius marched with them to Londinium, which he made his base. There, he began to deal with the invaders:[3]

There he divided his troops into many parts and attacked the predatory bands of the enemy, which were ranging about and were laden with heavy packs; quickly routing those who were driving along prisoners and cattle, he wrested from them the booty which the wretched tribute-paying people had lost. And when all this had been restored to them, except for a small part which was allotted to the wearied soldiers, he entered the city, which had previously been plunged into the greatest difficulties, but had been restored more quickly than rescue could have been expected, rejoicing and as if celebrating an ovation.

— Ammianus Marcellinus, Res Gestae 27.8.6

An amnesty was promised to deserters, which enabled Theodosius to regarrison abandoned forts. A new Dux Britanniarum was appointed, Dulcitius, with Civilis granted vicarius status to head a new civilian administration.[8]

After discovering that the local areani had collaborated with the invaders, Theodosius removed them from their positions.[9]

By the end of the year, the barbarians had been driven back to their homelands; the mutineers had been executed; Hadrian's Wall had been retaken and order had returned to the diocese. Under Civilis' rule the last of the earlier invaders were temporarily driven out in AD 369,[10] possibly using troops under his own personal command, and a program of civil restoration begun.

Theodosius also overcame and defeated the force of Valentinus, a Pannonian who had been exiled to Britain and joined the invaders.[9]

Considerable reorganization was undertaken in Britain, including the creation of a new province, Valentia, probably to better address the state of the far north. The poet Claudian suggests that naval activity took place in northern Britain.

It is possible that Theodosius mounted punitive expeditions against the barbarians and imposed terms upon them. Certainly, the Notitia Dignitatum later records four units of Attacotti serving Rome on the Continent. The areani were removed from duty and the frontiers refortified with co-operation from border tribes such as the Votadini, which marked the career of men such as Paternus.

Political effects[edit]

Theodosius returned to Rome a hero and was made senior military advisor to Valentinian to replace Jovinus. A decade later, his son became emperor.

The Romans had ended much of the chaos, but raids by all of the people listed above continued.

Fictional references[edit]

Fictional accounts of the Great Conspiracy were featured in Wallace Breem's historical novel Eagle in the Snow, Peter Vansittart's historical novel Three Six Seven: Memoirs of a Very Important Man, Stephen R. Lawhead's fantasy novel Taliesin, M. J. Trow's Britannia series, Jack Whyte's fantasy-historical novel The Skystone, and Mark Chadbourn's novel Pendragon, written under the pen-name James Wilde.

The author Francis Hagan utilises the Great Conspiracy as the backdrop for his trilogy of books in the Sabinus Chronicles (The Unquiet Shore, The Reaping of the Sea and The Vengeful Tide). In the novels a former Tribune, Sabinus, brings Roman and Barbarian forces together to save Rome from itself.


  1. ^ Hughes, Ian (2013). Imperial Brothers: Valentinian, Valens and the Disaster at Adrianople. Pen & Sword Military. p. 56. ISBN 978-1848844179.
  2. ^ Hughes p. 58-59.
  3. ^ a b c "The Roman History of Ammianus Marcellinus". Bill Thayer's Web Site. Retrieved 5 December 2016.
  4. ^ Hughes p. 58.
  5. ^ Hughes p. 56-61.
  6. ^ Hughes p. 69.
  7. ^ Hughes p. 71.
  8. ^ Jackson, Rupert M. (2021). The Roman occupation of Britain and its legacy. London. ISBN 978-1-350-14940-3. OCLC 1155483851.{{cite book}}: CS1 maint: location missing publisher (link)
  9. ^ a b Hughes p. 85
  10. ^ "Revealed: The story of the silk and gold clad woman buried in London's Spitalfields 1,600 years ago". The Independent. 2020-12-17. Retrieved 2022-03-22.


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