ROME AND PERSIA

Any description of the eastern frontier must start with a discussion of the relationship between Rome and Persia. The current period is marked by several clearly distinct stages: tension and intermittent warfare from 337 till 363, Julian's major campaign into Mesopotamia in 363 with the subsequent peace settlement, and, finally, the brief war of 421–2. The immediate cause of the chronic strain between the two empires in the fourth century must originate in the territorial gains achieved by Rome in the settlement of 298–9. As a result of this Roman victory, her sovereignty now extended beyond the Tigris and thus reached farther eastward than the empire ever achieved at any other time. Persia also recognized Roman sovereignty in Armenia and Iberia (modern Georgia). Rome gained control over all the important cities in north-eastern Mesopotamia: Amida, Nisibis, Singara and Bezabde. However, the Parthian and, later, Persian kingdom never accepted a permanent Roman presence in Mesopotamia east of the Euphrates. This, then, naturally led to renewed warfare, although it took several decades for hostilities to be resumed.

When Shapur II (309–79) became king of Persia he repudiated the settlement of 298, sending an embassy (probably in 334) to demand frontier changes. Following Constantine's refusal, Shapur abducted Diran, king of Armenia, violating the agreement. Constantine reacted by nominating his nephew Hannibalianus as the new king. In 336 Hannibalianus drove the Persians out of Armenia, and at least one source mentions Persian incursions launched into Roman territory. Hannibalianus was killed in 336 and succeeded, in 338, by a Roman vassal, Arsak (Arsaces), of doubtful loyalty. Constantine was preparing for a major campaign when he died in May 337. This was clearly planned as a large-scale expedition into Persia, similar to many in the second and third centuries.