Shahpur II (310-379) was a Persian king during whose reign the Sassanian dynasty reached a new height in military power and territorial expansion.
Posthumous son of Hormozd II, Shahpur was elected king before his birth, or possibly as an infant. During his minority reign Persia had a weak government of regents and suffered raids from its neighbors, particularly the Arabs who invaded southern Persia. Rome, however, which had gained some of the western Persian cities in Mesopotamia during the reign of Narse, Shahpur's grandfather, left Persia in peace.
Once grown up, Shahpur proved a formidable soldier and a capable ruler. After subduing the Arabs and conquering Bahrain on the southern littoral of the Persian Gulf, he turned his attention to his western frontiers with a view to restoring the Persian provinces lost earlier to Rome and establishing Persian power over Armenia and Iberia. Perso-Roman relations had latterly become further complicated by the conversion to Christianity of the Armenian king Terdat and by Emperor Constantine's proclaiming himself a protector of the Christians.
In the military operations which ensued, Shahpur had achieved a measure of success when, about 350, raids by the Huns drew his attention to the eastern frontiers. His successful campaign against the Huns (350-357) resulted in the expansion of the eastern boundaries and the inclusion of Hunnish contingents in the Persian army. Relieved of the problems of the East, Shahpur now turned his whole attention to Rome, demanding in a letter to Constantine the restoration of the lost Persian provinces. This led again to a series of wars which began in 359 and continued into 363, when Julian, the Roman emperor, despite the initial successes which took his armies to the gates of Ctesiphon, was forced to retreat and died of battle wounds on the way.
The peace treaty signed in 363 with Julian's successor, Jovian, rewarded Shahpur's skill and tenacity of purpose and was a severe blow to the Roman influence in the East. The five provinces beyond the Tigris, as well as the fortified city of Nisibi, the center of Rome's operations on its eastern frontiers, were returned to Persia, and Armenia was placed outside the sphere of Roman influence. Rome also agreed to cooperate with Persia in the upkeep of fortifications in the Caucasus in order to ward off Barbarian invasions.
During Shahpur's reign the Christians of Iran, who had been drawn into the Perso-Roman conflict, became the subject of renewed persecutions, which seem to have been motivated more by political consideration than by religious prejudice. On the other hand, Shahpur is reported to have been kind to the Jews.
Shahpur is considered one of the mightiest of the Sassanian kings. Of an imperious nature, he was tall in stature and strongly built. His title, Dhu'l-Aktaf (Lord of the Shoulders), may refer to his being broad-chested. His long reign of about 70 years coincided with the reign of 10 Roman emperors, beginning with Galerius and ending with Valentinian II.
Further Reading on Shahpur II
George Rawlinson discusses the reign of Shahpur II, mainly on the basis of classical sources, in his The Seventh Great Oriental Monarchy (1876), as does Percy Sykes in A History of Persia (2 vols., 1915; rev. ed. 1930).