Perso-Roman wars of 337–361

The Perso-Roman wars of 337–361 were a series of military conflicts fought between the Roman Empire and the Sasanid Empire between 337 and 361. They were a result of long-standing aggression between the rival powers over influence in the border kingdoms of Armenia and Iberia, as well as the desire of Shapur II, after his Arab campaign, to revoke the unfavorable terms of the Treaty of Nisibis, which had concluded the previous war between the empires. Though the Romans under Constantius II were defeated in several sanguinary encounters, Shapur was unable to secure a decisive victory.

First war:337-350
In preparation for a campaign against the Sasanid Empire, Emperor Constantine sent his son Constantius to Antioch. In 336, Shapur II sent his general Narses to invade Armenia. With the help of the Vitaxa of Aljnik, he captured Amida, defeating Constantius there and at Constantia. Narses, however, was later defeated and killed at a battle against Constantius at Narasara. Following Emperor Constantine's death, Shapur besieged Nisibis, which was then regarded as the key to Mesopotamia. After sixty days, no closer to taking Nisibis and with a plague hampering his army, he lifted the siege and returned to Persia. Although he lost at Nisibis, Shapur collected tribute from the Armenian king Khosrov starting in the year 345/6.

In 346/7 Shapur besieged Nisibis a second time, and was repulsed. In 343/344/348 Shapur met Constantius in a battle near Singara. During the night the larger part of the Sasanid army, which had been held back by Shapur as a reserve, emerged unexpectedly from behind the overlooking heights, and routed the Romans.

In 350, Shapur laid siege to Nisibis, for a third time. The dams of the river Mygdonius, which passed near the valley in which Nisibis was located, were broken down, and the valley flooded. When the whole plain was filled with water up to the walls of the city, a Sasanid fleet was embarked and floated to the ramparts. A part of the walls collapsed and the Sasanids withdrew in preparation for the assault. The attack which was launched, supported by Sasanid war-elephants, bogged down in the muddy waters formed by the lake, and Shapur gave the signal to fall back. In the interval of a single night the defenders effected the repair of the walls, this along with news of Hunnic invasions of the eastern provinces, compelled Shapur to a cessation of hostilities against Rome. Before retreating to Persia, Shapur burned all his siege equipment and executed some of his chief officers and advisors.

The usurpation of Magnentius in the west occurred around the same time diverting Constantius, who left his cousin Gallus to defend the east.

Interwar:350-359
During 350-359 the war between the Roman and Sasanid Empires languished. Constantius was engaged in several campaigns against enemies, both foreign and domestic, while Shapur was occupied with his eastern campaign in the steppes of Central Asia.

In 356, however, the Romans made serious overtures towards a lasting peace. Shapur delivered his conditions to the following effect: that should Constantius deliver up the provinces of Mesopotamia and Armenia, which Diocletian had wrested from Narseh under the Treaty of Nisibis. Constantius, though discredited by previous defeats, and even himself secretly doubtful of the outcome of a second war, treated the offer with contempt. Yet, he dispatched civil and military officers accompanied by a sophist on a new embassy to the Sasanid court, advising Shapur II of the necessity of more reasonable grounds for peace. The embassy was dismissed by Shapur when he arrived at Ctesiphon and preparations were conducted for another campaign.

Second war:359-361
Shapur II, in the campaign of 359, was directed by the Roman renegade Antoninus. With eastern tribes now supporting his army, Shapur avoided besieging fortress cities of Mesopotamia, choosing instead to cross the Euphrates and marched toward the city of Amida.

As soon as Ursicinus' spies had informed him the Sasanid army was on the march, he secured the defenses of Nisibis. From there he proceeded to Amida, a city recently fortified by Constantius II. After giving orders for the fields of Roman Mesopotamia to be burned to prevent Shapur's army using it as fodder, the population evacuated into the fortified cities. With Shapur's crossing of the Euphrates secured, Ursicinus fell back to Amida. In the meantime the Sasanid army had crossed the Tigris. Ursicinus, retreated in haste to oversee the defense of the Euphrates, was intercepted on the march by Sasanid cavalry, barely escaping. His body-guard was dispersed, and in the chaos the survivors were driven into Amida, which was blockaded by the Sasanid vanguard. Six Roman legions, the 13th, 10th, 5th Parthian legion and two rebel Gallic legions of Magnentius, whom Constantantius had sent east at the end of the civil war, had taken shelter in the city, bringing the numbers to 50,000. The army of Shapur reportedly numbered 120,000 men.

Shapur bypassed Nisibis and reached Bebase. From there, his scouts informed him of the flooding of the Euphrates and a strong Roman fortification on the other bank. Faced with this predicament, Antoninus advised the Sasanid monarch to force march his army and cross the Euphrates northwest of Amida. From there Shapur could advance into the interior of Asia Minor. Marching by way of Horre, Miacarire, Carcha, and the fortresses of Reman and Busan which capitulated on his approach, Shapur arrived beneath the walls of Amida at the end of July.

Siege of Amida (359)


Shapur convinced himself that the mere sight of his formidable army would terrorize the city into surrender. Grumbates, king of the Chionites, was sent to threaten the defiant city into submission. But before the king could make known the reason of his approach, a dart from the Roman ballistae struck his son and crown prince killing him instantly.

The Sasanids encircled the city on every side; as auxiliaries, the Vertae were assigned the assault of the south wall, the Albanians on the north, the Chionites to the east, and the Segestans with their war-elephants on the west. The operations of the siege began with a two-day mutual discharge of missiles, following heavy casualties on both sides, a truce was concluded. The Sasanids then set themselves to raising mounds for scaling the walls, and siege towers captured from the Romans in the previous war at Singara. Meanwhile, the forays of the Sasanid cavalry were devastating the surrounding country taking many prisoners and much spoils. Ursicinus, who proposed a bold attack using light infantry to divert the Sasanid blockade, was accused of fomenting a treacherous reverse through his excessive zeal for the relief of the city.

A night attack on the Sasanid camp by two Gallic legions from Amida boosted Roman morale and inflicted heavy losses on the Sasanid army, but the loss of 400 Gauls was more devastating to the besieged city. Shapur increased his assaults on the city only to suffer further casualties due to the Roman scorpions and fire darts. Finally the Roman structures, under the bombardment of Sasanid ballistae, collapsed. The Sasanids carried their earth mounds to the level of the ramparts, and swarmed into the city. After a prolonged last-ditch defense the garrison was overpowered, the city sacked and the inhabitants removed to the further reaches of the Sasanid Empire. Count Aelianus and the rest of the surviving Roman commanders were crucified. The siege being successful and autumn arriving, the Sasanids were obliged to return to winter-quarters.

Campaigns of 360
In spring 360, Shapur renewed his inroads into Mesopotamia, besieging the desert town of Singara. The wall was breached after some days by battering ram, and the town fell. The 1st Flavian and 1st Parthian legions which had formed the garrison, as well as the inhabitants of Singara, were sent into captivity in Sasanid Persia.

Shapur then invested Bazabde, a strong Roman fortress on the Tigris. He lingered only to repair the walls and post a strong garrison in Bazabde before he proceeded on an expedition against Virtha, a formidable fortress on the outliers of the Mesopotamian desert. But the garrison of Virtha defended themselves successfully and Shapur retired over the Tigris towards the end of the campaign season.

In the meantime, towards autumn of 360, Constantius finally arrived at the head of his long-prepared army. The revolt of Julian in Gaul had momentarily delayed the emperor, but his ministers prevailed on him to campaign against the Sasanids. Before crossing the Tigris to face Shapur, Constantius was determined to retake the important fortress of Bazabde. During the ensuing blockade, the Sasanids sallied several times from the city to destroy Roman battering rams and ballistae. With winter beginning, the area was flooded with heavy rains and Constantius' attacks were beaten back, he retreated from Bazabde into Syria and wintered in Antioch.

Campaigns of 361
The following spring 361, Constantius crossed the Euphrates once more, arriving at Edessa. Unwilling to resume the blockade of Bazabde and fearing a costly siege, he sent his two generals, Arbetio and Agilo, to observe the motions of Shapur from the further bank of the Tigris to inform him when the latter should cross the river. Shapur, however, declined to venture over the Tigris and the entire summer of 361 was wasted in ineffectual maneuvering with each monarch on opposite banks of the river. This war ended indecisively with Constantius dying of fever on 5 October 361 in Mobsucrenae.