In considering the question of among whom Christianity first found acceptance in Mesopotamia, four groups of people are relevant: first, the numerically significant Jewish Diaspora; and, second, the native Arameans, Assyrians, and Chaldeans of northern Mesopotamia, to whom the Persians came towards the end of the third century. Beginning in the mid-third century additional Christian refugees streamed into the empire of the Sassanians, as they fled the persecutions of of the Roman emperors Decius in 250, Valerian in 257-258 and Diocletian in 303-304. The fourth numerically important group were the Roman and later Byzantine prisoners of war and deportees, whom the Sassanian kings resettled in their empire, again beginning in the mid-third century. For instance, in 260 Shapur I (ruled 240-272) laid waste to Syria, Cilicia, and Cappadocia and conquered Antioch, from which he deported tens of thousands of Christians, including Bishop Demetrius, and resettled them in Mesopotamia and the ancient province of Susiana.
Baumer, The Church of the East, p. 23
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Entrusted to the Dirt 
Very interesting, thank you! Just read more on Shapur I, sounds like a wise, compassionate and reasonable man especially for those days!
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