The standard view of early Christianity in Persia is that it was tolerated until
Constantine the Great (r. 306–337) was converted to Christianity. In a letter to Shapur II, tansmitted by
Eusebius in his
Vita Constantini he asks Shapur to treat the Christians well. Shapur II then became suspicious of Christians in his empire, and after being defeated in a war with Rome ordering that the Christian churches be destroyed and their clergy executed. This was later extended to execution of all Christians. This view is based on
Syriac accounts of martyrdoms which might exaggerate the extent. The theme of Shapur's persecution being a reaction to Constantine's conversion emerged only during the reign of
Theodosius II (r. 402–450), and must be treated with some skepticism. However, there is no doubt that Shapur II severely persecuted the Christians from 339 until his death in 379, and the 5th-century Syriac
Passions most likely were the source for
Sozomenos's account in his
Ecclesiastical History, and have been carried forward into Greek translations. ==Sozomen's account==