ADIABÈNE (Hadyab, native name; Gr. 'Αδάβην). — Region situated on the left bank of the Tigris, with Arbela as its ecclesiastical capital, inhabited by a population of predominantly Aramaic origin; the literary language was Aramaic.
The first concrete information about Christianity in Adiabene is found in the Acts of the martyrs killed during the persecution of Shapur II in the second half of the 4th century. However, it must be believed that there were already Christians in the ecclesiastical province of Arbela at the beginning of the 3rd century, since the Liber Legum Regionum (ed. in Patrologia Syriaca, II, 608) attests to their presence in Persia. Indeed, everything suggests that Christianity had penetrated Adiabene early on through the Jews. Their influence was so great there that Helena, sister and wife of Monobazus I, and her son Izates, converted to Judaism around the year 30 of the Christian era (Flavius Josephus, Antiquitates Iudaicae, XX, 2-4). Moreover, relations between Jerusalem and Adiabene were then very close, as evidenced by the fact that Izates sent his five sons there for their education, and Queen Helena traveled there around the year 44 and had a mausoleum built for herself.
Apart from the not entirely reliable information provided by the Chronicle of Arbela, it is clear that by the mid-4th century St. John, martyred in 344, was bishop of Arbela, and that he was succeeded by St. Abraham, also martyred in 345. The considerable number of martyrs demonstrates that Christianity had by then taken firm root and spread widely.