Objectives Ever since the "humiliating"
Peace of Nisibis concluded between Shapur's grandfather
Narseh and the Roman emperor
Diocletian in 298, the borders between the two empires had changed largely in favor of the Romans, who in the treaty received a handful of provinces in
Mesopotamia, changing the border from the
Euphrates to the
Tigris, close to the Sasanian capital of
Ctesiphon. The Romans also received control over the kingdoms of
Iberia and
Armenia, and gained control over parts of upper
Media in Iran proper. Shapur's primary objective was thus to nullify the treaty, which he spent much of his reign trying to accomplish. Another cause for Shapur's wars against the Romans was their attempts to meddle in the domestic affairs of the Sasanian Empire and hurt Shapur's kingship by supporting his brother
Hormizd, who had been well received at the Roman court by
Constantine the Great and made a cavalry commander. Shapur had made fruitless attempts to satisfy his brother, even having his wife sent to him, who had originally helped him escape imprisonment. However, Hormizd had already become an avid
philhellene during his stay with the Romans, with whom he felt at home. Another reason was Constantine's declaration of Christianity as the official religion of the Roman Empire in 337. He had also declared himself the defender of all the Christians in the world, including those living in the Sasanian realm.
Early campaigns and first war against the Romans In 337, after the accession of
Constantius II to the Roman throne, Shapur II, provoked by the Roman rulers' backing of Armenia and the Armenian kingdom's earlier
conversion to Christianity, broke the peace concluded in 298 between
Narseh (293–302) and
Diocletian (284–305), which had been observed for forty years. Most of the fighting during this campaign occurred in Roman Mesopotamia, where Roman fortifications impeded the Persian advance. Nevertheless, Shapur was able to take some forts, such as Vitra. Persian forces also devastated Armenia and captured and blinded the Armenian king
Tiran, perhaps in 350. Shapur besieged the Roman fortress city of
Nisibis in Mesopotamia thrice (in 338, 346, and 350) and was repulsed each time. During this campaign, the sole engagement between the sides' main armies was the
Battle of Singara (modern-day
Sinjar, Iraq) in 344, where Persian forces feinted a retreat and inflicted significant losses on the Roman army. Neither side managed to achieve a decisive advantage, and an invasion of Central Asian nomads in the east forced Shapur to abandon his campaign against Rome by 350. These nomads were likely the
Kidarites, who were threatening the
Gupta Empire (320–500 CE) in India at the same time. After an extended campaign against the nomads, Shapur forced their king,
Grumbates, into an alliance, thus gaining a new ally against the Romans. In particular, Grumbates's forces joined the Persians in the
Siege of Amida in 359.
Second war against the Romans and invasion of Armenia to
Antioch (in 362) and his Persian expedition (in 363), ending with his death near
Samarra In 356, Shapur rejected a peace overture by Constantius, replying that Rome should return Armenia and other territories lost by Persia in the Treaty of Nisibis. In 359, Shapur II invaded southern Armenia and besieged the fortress of
Amida (now
Diyarbakır, Turkey). He was joined by King Grumbates's forces and other allies. Amida surrendered after a seventy-three-day siege. The city was plundered and its inhabitants were deported to Khuzistan. The delay forced Shapur to halt operations for the winter. Early the following spring he continued his operations against the Roman fortresses, capturing
Singara and
Bezabde (
Cizre?), again at a heavy cost. In the next year
Constantius II launched a counterattack, having spent the winter making massive preparations in
Constantinople; Shapur, who had meanwhile lost the aid of his Asianic allies, avoided battle, but left strong garrisons in all the fortresses which he had captured. Constantius laid siege to Bezabde, but proved incapable of taking it, and retired on the approach of winter to
Antioch, where he died soon after. Constantius was succeeded by his cousin
Julian (361–363), who came to the throne determined to avenge the recent Roman reverses in the east. Though Shapur attempted an honorable reconciliation, warned of the capabilities which Julian had displayed in wars against the
Alemanni in
Gaul, the emperor dismissed negotiation. showing
Mithra, Shapur II, and
Ahura Mazda above a defeated Julian, lying prostrate In 363 Julian, at the head of a strong army, advanced to Shapur's capital city of
Ctesiphon and defeated a presumably larger Sasanian force at the
Battle of Ctesiphon; however, he was unable to take the fortified city, or engage with the main Persian army under Shapur II that was approaching. Julian was killed by the enemy in a skirmish during his retreat back to Roman territory. His successor
Jovian (363–364) made an ignominious peace in which the districts beyond the
Tigris which had been acquired in 298 were given to the Persians along with Nisibis and Singara, and the Romans promised to interfere no more in Armenia. The great success is represented in the rock sculptures near the town
Bishapur in Pars (Stolze,
Persepolis, p. 141); under the hooves of the king's horse lies the body of an enemy, probably Julian, and a supplicant Roman, the Emperor Jovian, asks for peace. According to the peace treaty between Shapur and Jovian,
Georgia and Armenia were to be ceded to the Sasanians, and the Romans forbidden from further involvement in the affairs of Armenia. The Armenian King
Arshak II, who had joined Julian's campaign, was lured to Persia and imprisoned in the
Castle of Oblivion (Armenian: ) in
Khuzistan. Shapur destroyed many towns in Armenia and deported their inhabitants to Persia. He persecuted the local Christians, erected
fire temples and forced conversion to
Zoroastrianism. The Persians were assisted in Armenia by the magnates
Meruzhan Artsruni and Vahan Mamikonian, who were made governors of the country and one of whom was given Shapur's own sister in marriage. However, the Armenian nobles resisted him successfully, secretly supported by the Romans, who sent King
Pap, the son of Arshak II, into Armenia. Shapur personally invaded Armenia in response to Pap's return, although Pap was restored to the Armenian throne again with the help of a Roman army in approximately spring 370. Persian forces were defeated by a joint Roman-Armenian army in 371, and an army led by Shapur himself was defeated in another battle on the eastern border of Armenia. Eventually, Pap was suspected of colluding with the Persians and was assassinated in 375 by the order of the Roman emperor
Valens. Shapur and Valens negotiated inconclusively over the status of Armenia until 377, and Valens's defeat and death at the
Battle of Adrianople in 378 ended Roman presence in Armenia. Armenia was left in peace for the time being. The country was later partitioned between Rome and Persia in 387, under Shapur's son
Shapur III. In Georgia, then known as
Iberia, where the Sasanians were also given control, Shapur II installed
Aspacures II of Iberia in the east; however, in western Georgia, Valens also succeeded in setting up his own king,
Sauromaces II of Iberia. Shapur II had conducted great hosts of captives from the Roman territory into his dominions, most of whom were settled in
Elam. Here he rebuilt
Susa—after having killed the city's rebellious inhabitants. ==War in the East==