Cath. since 605. Grigor originated from Prat d-Mayshan. Prior to his election he was a teacher of biblical interpretation at the School of Seleucia. The Persian authorities, or more specifically Queen Shirin, are said to have intervened in his election. One of the main internal problems Grigor had to deal with was the crisis in the School of Nisibis surrounding the controversial leadership of Ḥenana of Adiabene. The synod convened by Grigor in 605 fully endorsed the commentaries (puššāqe) and writings of Theodore of Mopsuestia as the main and even the sole authority, against which no one had the right to introduce alternative views. This strong statement must have targeted Ḥenana and his followers. Other decisions of the synod deal with the problem of wandering or independent monks, both male and female, and with the need to bring monasteries under episcopal authority.

After Cath. Grigor’s death, which occurred between 608 and 611 (Vööbus, 316–7), the patriarchal throne was vacant until 628 (the death of Emperor Khusrau II). During this nearly twenty-year long interregnum, Babai the Great and Aba, Archdeacon of Seleucia, were in charge of the administration of the Ch. of E. From this period the Synodicon Orientale preserves a profession of faith that the bps. prepared for the Persian Emperor, in the context of a disputation with the Syr. Orth. (612).