In the year 363 the Roman Emperor
Julian, hoping to avenge Roman defeats under his predecessor
Constantius II and to establish his fame by accomplishing what had never been done by a Roman before - the subjugation of the east - invaded the dominions of
Shapur II, king of
Persia. Assembling his strength at
Carrhae in the Roman province of
Mesopotamia, Julian divided his forces. While a part of the army (30,000 men, according to
Ammianus Marcellinus) was dispatched north-east under his cousin
Procopius and Count Sebastian to enlist the aid of
Arshak II of Armenia for a march down the
Tigris to
Ctesiphon; Julian himself, with a larger force (65,000), penetrated
Assyria to the south, proceeding along the
Euphrates from
Callinicum with the same ultimate destination. Julian crossed the frontier at
Circesium, where it had been established by the peace of
Diocletian, leaving a detachment of 10,000 to secure his rear. In response to the Roman's invasion, Sasanian cavalry harried his wings, and the dykes and canals were released to flood the country, the land was scorched. However, these obstacles were surmounted.
Anah surrendered and was burned, Macepracta was subdued, and after a journey of five days Julian's army came upon the city of Hit. Its soldiers had fled and the city, containing mostly women and children were slaughtered.
Pirisabora was reduced, sacked, and its inhabitants massacred. The day following the fall of Pirisabora, a Roman reconnaissance unit was surprised and defeated in an ambush. Julian removed its commanders from their positions of authority. As the Romans approached the Tigris, they discovered a city that had been deserted by its Jewish residents, and the soldiers set it on fire. Julian promptly arrived under the walls of Maiozamalcha on 8 May, a strongly fortified place 11 miles from the Sasanian capital of
Ctesiphon. A cursory reconnaissance of the city walls by Julian was attacked by a small contingent of Sasanians, nearly killing the emperor. ==The siege==