MĀR ĀBĀ I. — Nestorian patriarch, born at Hâlê on the Tigris, ordained at the beginning of 540 and died on 29 February 552. Converted to Christianity while employed as a civil servant, he attended the theological school at Nisibi, learned Greek, and visited Palestine, Egypt, Greece, and Constantinople, where around 525 he became acquainted with Cosmas Indicopleustes.
Returned to Nisibi, he taught there until elected katholikòs. He worked for reconciliation, ventured as far as Persian Elam, and founded the theological school at Seleucia-Ctesiphon. The Magi obtained (541) from the Emperor Mār Ābā’s exile; he gathered around himself an assembly of bishops to codify decrees and canons. In 548 he fled to Seleucia but was arrested; after three years, however, Khosrow I released him to send him to quell a revolt by his son, a task he successfully accomplished.
A compendium of matrimonial law by Mār Ābā survives (ed. E. Sachau, *Syrische Rechtsbücher*, III, Berlin 1914, pp. 255–58).