First recorded bp. of Nisibis. Although Yaʿqub’s name appears in a variety of late antique sources, trustworthy historical data about him are quite limited. The closest we have to an eyewitness report of Yaʿqub are the ‘Nisibene Hymns’ (13–16: CSCO 218–219) of Ephrem. In the Hymns, which were most likely written ca. 359, Yaʿqub is identified as ‘Father’ of the church of Nisibis, to which ‘he gave birth and whose infancy he nourished with milk’ (14:21). Yaʿqub reared the church, ‘dealing with her as a child, loving her, and teaching her piety’ (14:18). Yaʿqub, who was known for his eloquence (14:15) may have been an early example for Ephrem in his subsequent role as teacher and poet. Finally, Yaʿqub’s burial place in Nisibis ‘protected Nisibis ... during the time of her pruning’ (13:19–20). Yaʿqub may well have been recognized as a charismatic figure even before his death. It was this early reputation which laid the groundwork for Armenian and Greek legends that came to dominate his historical memory: while no authentic works were preserved under his name, he would be identified as the author of the ‘Demonstrations’ now known to be the work of Aphrahaṭ, of apocryphal Letters addressed to Cath. Papa of Seleucia, and of the spurious ‘Canons of Nicea’. In Armenian tradition he came to be revered as a founder of Armenian Christianity and a relative of Gregory the Illuminator. Yaʿqub is also widely seen as one of the bps. who participated in the Council of Nicea (325).

Historiographical problems relating to the figure of Yaʿqub are complicated by the elaboration of what purport to be historical reports from the 4th and 5th cent. Alongside the quite generalized remarks of Ephrem, the reports of Theodoret of Cyrrhus, in the ‘History of the monks of Syria’, and of Gennadius, in the ‘Epic Histories’, contributed to the subsequent legend of Yaʿqub as a holy man and a model of the episcopacy. This material, which is more of the nature of hagiography than history, is nonetheless important for tracing the development of traditions related to the growing cult of Yaʿqub and to tensions surrounding the emerging concept of the episcopacy.