Mar Yahbalaha III, an ethnic Uighur and a monk of the Ch. of E., was born in the vicinity of Khān Bālīq (Beijing). As a young monk, he took the name Markos and became devoted to his spiritual master, Ṣawma. Sometime around 1275 the two of them set out on a pilgrimage with the intention of visiting Jerusalem. In spite of travel permits from Kublai Khan, the two encountered numerous difficulties before reaching Baghdad and meeting with the cath. of the Ch. of E., Mar Denḥa. When the cath. died (1281), Markos was chosen as his successor and took the name Mar Yahbalaha III. His electors may have hoped that by raising someone from the East to the patriarchal throne they would gain some advantage with their Mongol overlords.

Mar Yahbalaha is remembered for his efforts to establish diplomatic contacts with the Mongols and for his defense of the Ch. of E. against harassment and massacres by local Muslim rulers. Despite valiant efforts, Yahbalaha witnessed the decimation of his Church. A particularly savage massacre of Christians took place at Arbil (Arbela). These sad events in the history of the Ch. of E. were recorded by Ṣawma who also kept a record of his diplomatic mission to Christian Europe. The story of Mar Yahbalaha first became known in the English-speaking world in 1928. In that year the British orientalist E. A. Wallis Budge published his Monks of Kublai Khan, Emperor of China.