MĀR ĀBĀ I. - Nestorian patriarch, b. at Ḥālè near the Tigris, ordained at the beginning of 540 and d. 29 Feb. 552. Converted to Christianity while employed as a clerk, he attended the theological school of Nisibis, learned Greek, and visited Palestine, Egypt, Greece, and Constantinople, where around 525 he became acquainted with Cosmas Indicopleustes.
Having returned to Nisibis, he taught there until he was elected katholikós. He worked for reconciliation, travelled as far as Elam in Persia, and founded the theological school of Seleucia-Ctesiphon. The magi obtained from the Emperor (541) the exile of M. A., who gathered around himself an assembly of bishops intended to codify decrees and canons. In 548 he fled to Seleucia, but was arrested, until after 3 years Chosroes I freed him in order to send him to quell the revolt of his son, a task he successfully accomplished.
Of M. A. there survives a compendium of matrimonial law (ed. E. Sachau, Syrische Rechtsbücher, III, Berlin 1914, pp. 255-58).