After the death of Hormuzd II. (302-31o), the son of Narses, the magnates imprisoned or put to death his adult sons, one of whom, Hormisdas, later escaped to the Romans, who used him as a pretender in their wars. Shapur II., a posthumous child of the late king, was then raised to the throne, a proof that the great magnates held the sovereignty in their own hands and attempted to order matters at their own pleasure. Shapur, however, when he came to manhood proved himself an independent and ener getic ruler.
Shapur II.—Meanwhile the Roman empire had become Chris tian, the sequel of which was that the Syro-Christian population of Mesopotamia and Babylonia—even more than the Hellenic cities in former times—gravitated to the west and looked to Rome for deliverance from the infidel yoke. On similar grounds Christianity, as opposed to Mazdaism enforced officially by the Sassanids, became predominant in Armenia. Between these two great creeds the old Armenian religion was unable to hold its own; as early as A.D. 294 King Tiridates was converted by Greg ory the Illuminator and adopted the Christian faith. For this very reason the Sassanid empire was the more constrained to champion Zoroastrianism. It was under Shapur II. that the com pilation of the Avesta was completed and the state orthodoxy perfected by the chief mobed, Aturpad. All heresy was pro scribed by the state, defection from the true faith pronounced a capital crime, and the persecution of the heterodox—particu larly the Christians—began (cf. Sachall, "Die rechtlichen Ver haltnisse der Christen in Sassanidenreich," in Mitteilungen des Seminars fiir orientalische Sprachen fur Berlin, Bd. X., Abt. 2, 1907). Thus the duel between the two great empires now becomes simultaneously a duel between the two religions.
In such a position of affairs a fresh war with Rome was in evitable.' It was begun by Shapur in A.D. 337, the year that saw the death of Constantine the Great. The conflict centred round the Mesopotamian fortresses; Shapur thrice besieged Nisibis without success, but reduced several others, as Amida (359) and Singara (36o), and transplanted great masses of inhabitants into Susiana. The emperor Constantius conducted the war feebly and was consistently beaten in the field. But, in spite of all, Shapur found it impossible to penetrate deeper into the Roman territory. He was hampered by the attack of nomadic tribes in the east, among whom the Chionites now begin to be men tioned. Year after year he took the field against them (353 358), till finally he compelled them to support him with aux iliaries (Ammian. Marc. 14, 3 , 16, 9; 5; 18, 4, 6). With
this war is evidently connected the foundation of the great town New-Shapur (Nishapur) in Khorasan.
By the resolution of Julian (363) to begin an energetic at 'For the succeeding events see also under ROME: Ancient History; and articles on the Roman emperors and Persian kings.
tack on the Persian empire, the conflict, after the lapse of a quarter of a century, assumed a new phase. Julian pressed forward to Ctesiphon but succumbed to a wound ; and his suc cessor Jovian soon found himself in such straits, that he could only extricate himself and his army by a disgraceful peace at the close of 363, which ceded the possessions on the Tigris and the great fortress of Nisibis, and pledged Rome to abandon Armenia and her Arsacid protégé, Arsaces III., to the Persian.
Shapur endeavoured to occupy Armenia and introduce the Zoroastrian orthodoxy. He captured Arsaces III. by treachery and compelled him to commit suicide ; but the Armenian mag nates proved refractory, placed Arsaces's son Pap on the throne, and found secret support among the Romans. This all but led to a new war ; but in 374 Valens sacrificed Pap and had him killed in Tarsus. The subsequent invasions of the Goths, in battle with whom Valens fell at Adrianople (375), definitely precluded Roman intervention ; and the end of the Armenian troubles was that (c. 39o) Bahram IV. and Theodosius the Great concluded a treaty which abandoned the extreme west of Armenia to the Romans and confirmed the remainder in the Persian possession. Thus peace and friendship could at last exist with Rome ; and in 408 Yazdegerd I. contracted an alliance with Theodosius II. In Armenia the Persians immediately removed the last kings of the house of Arsaces (430), and thenceforward the main portion of the country remained a Persian province under the control of a marzban, though the Armenian nobles still made re peated attempts at insurrection. The introduction of Zoroas trianism was abandoned; Christianity was already far too deeply rooted. But the sequel to the Roman sacrifice of Armenian in terests was that the Armenian Christians now seceded from the orthodoxy of Rome and Constantinople, and organized themselves into an independent national church. This church was due, be fore all, to the efforts of the Catholicos Sahak (390-439), whose colleague Mesrob, by his translation of the Bible, laid the foun dations of an Armenian literature (see ARMENIAN CHURCH).