Nestorian Christianity

The Church of the East (Syriac: ܥܕܬܐ ܕܡܕܢܚܐ‎ Ēdtāʾ d-Maḏenḥā), also known as the Nestorian Church, is a Christian church within the Syriac tradition of Eastern Christianity. It was the Christian church of the Sassanian Empire, and quickly spread widely through Asia. Between the 9th and 14th centuries, the Church represented the world's largest Christian church in terms of geographical extent, with dioceses stretching from the Mediterranean Sea to China and India. Several modern churches claim continuity with the historical Church of the East.

The Church of the East was headed by the Patriarch of the East, continuing a line that, according to tradition, stretched back to the Apostolic Age. Liturgically, the church adhered to the East Syrian Rite, and theologically, it adopted the doctrine of Nestorianism, which emphasises the distinctness of the divine and human natures of Jesus. This doctrine and its namesake, Nestorius (386–451), were condemned by the Council of Ephesus in 431, leading to the Nestorian Schism and a subsequent exodus of Nestorius' supporters to Sasanian Persia. The existing Christians in Persia welcomed these refugees and gradually adopted Nestorian doctrine by the 5th century, leading the Church of Persia to be known alternately as the Nestorian Church.

The church grew rapidly under the Sassanians, and following the Muslim conquest of Persia (633–654) it was designated as a protected dhimmi community under Muslim rule. From the 6th century it expanded greatly, establishing communities in India (the Saint Thomas Christians), among the Mongols in Central Asia, and in China, which became home to a thriving community under the Tang dynasty from the 7th to the 9th century. In the 13th and 14th centuries the church experienced a final period of expansion under the Mongol Empire, where influential Nestorian Christians sat in the Mongol court.

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