Pax Romana (Latin for "Roman peace") was the long period of relative peace and minimal expansion by military force experienced by the Roman Empire in the 1st and 2nd centuries AD. Since it was established by Caesar Augustus it is sometimes called Pax Augusta. Its span was about 207 years (27 BC to 180 AD).
Origins of the term 
The Pax Romana began with the accession of Augustus in 27 BC, which marked the end of the Roman Republic and its final civil wars, and lasted until 180 AD at the death of Marcus Aurelius. The Latin word pax, most often translated "peace," as in the nominative case in Latin, and also means "treaty" or "accord." The Roman legal system, which forms the basis of many Western court systems today, unified the administration of justice in the courts throughout the provinces. The Legions patrolled the borders with success, and though there were still many foreign wars, the internal empire was free from major invasion, piracy, or social disorder on any grand scale. The empire, wracked with civil war for the last century of the Republic and for years following the Pax Romana, was largely free of large-scale power disputes. Only the year 69 AD, the so-called 'Year of the Four Emperors' following the fall of Nero and the Julio-Claudian line, interrupted nearly 300 years of civil order. Even this was only a minor hiccup in comparison to other eras. The arts and architecture flourished as well, along with commerce and the economy.
The concept of Pax Romana was first described by Edward Gibbon in Chapter Two of The Decline and Fall of the Roman Empire. Gibbon proposed a period of moderation under Augustus and his successors and argued that generals bent on expansion (e.g. Germanicus, Agricola and Corbulo) were checked and recalled by the Emperors during their victories favouring consolidation ahead of further expansion. Gibbon lists the Roman conquest of Britain under Claudius and the conquests of Trajan as exceptions to this policy of moderation and places the end of the period at the death of Marcus Aurelius in 180 AD, despite the conclusion of peace by the latter's son Commodus later in the same year. During the Pax Romana, the area of Roman rule expanded to about five million square kilometres (two million square miles).
Pax Romana, according to Gibbon, would have ended with Commodus himself, whose dispendious excesses and despotic misrule destabilised central Roman politics amidst the chaos of the Germanic invasions of the Rhine-Danube frontier. Commodus's assassination led to a succession crisis, the so-called Year of the Five Emperors, which culminated in the ascension of a soldier-emperor, Septimius Severus, who, despite giving the Empire a peaceful reign, was accused by Gibbon of catalysing the Crisis of the Third Century, a period of economic, political and military crisis that, together with the Germanic invasions and the rise of the Sassanid Persian Empire in the East, almost led the Empire to collapse.
Beginnings of relative peace 
The Pax Romana started after Octavian (Augustus) defeated Mark Antony in the Battle of Actium. He became princeps, or "first citizen". Lacking a good precedent of successful one-man rule, Augustus created a junta of the greatest military magnates and stood as the front man. By binding together these leading magnates in a coalition, he eliminated the prospect of civil war. The Pax Romana was not immediate, despite the end of the civil wars, because fighting continued in Spain and in the Alps. Nevertheless, Augustus closed the Gates of Janus (the Roman ceremony to mark world Peace) three times, first in 29 BC and again in 25 BC. The third closure is undocumented, but Inez Scott Ryberg (1949) and Gaius Stern (2006) have persuasively dated the third closure to 13 BC with the Ara Pacis ceremony. At the time of the Ludi Saeculares in 17 BC the concept of Peace was publicized, and in 13 BC was proclaimed when Augustus and Agrippa jointly returned from pacifying the provinces. The Ara Pacis ceremony was no doubt part of this announcement.
Augustus faced a problem making peace an acceptable mode of life for the Romans, who had been at war with one power or another continuously for 200 years. Romans regarded peace not as an absence of war, but the rare situation that existed when all opponents had been beaten down and lost the ability to resist. Augustus' challenge was to persuade Romans that the prosperity they could achieve in the absence of warfare was better for the Empire than the potential wealth and honor acquired when fighting a risky war. Augustus succeeded by means of skillful propaganda. Subsequent emperors followed his lead, sometimes producing lavish ceremonies to close the Gates of Janus, issuing coins with Pax on the reverse, and patronizing literature extolling the benefits of the Pax Romana.
Similar terms 
Given the prominence of the concept of Pax Romana, historians have coined variants of the term to describe systems of relative peace that have been established, attempted or argued to have existed. Such times have been credited to the British Empire during the 19th century. Some variants include:
- Pax Americana
- Pax Britannica
- Pax Europaea
- Pax Hispanica
- Pax Mongolica
- Pax Ottomana
- Pax Sinica
- Pax Khazarica
- Pax Syriana
- "Pax Romana". Britannica Online Encyclopedia.
- Augustus states in Res Gestae 13 that he closed the Gates three times, a fact documented by many other historians (See Gates of Janus).
- Scott Ryberg, Inez (1949). "The Procession of the Ara Pacis". Memoirs of the American Academy in Rome 19: 79–101.
- Stern, Gaius (2006). Women, children, and senators on the Ara Pacis Augustae: A study of Augustus' vision of a new world order in 13 BC.. ProQuest. ISBN 978-0-549-83411-3.
- Sir Ronald Syme had suggested a later date (but Rome was then at war).
- Momigliano, Arnaldo (1942). "The Peace of the Ara Pacis". Journal of the Warburg and Courtauld Institutes 5: 228–231.