Sources: Council of Ephesus (431 AD) acts; Nestorius, The Bazaar of Heraclides (his defense, discovered 1895); Cyril of Alexandria, Letters; the Peshitta (Syriac Bible).

Nestorius (~386–451 AD), Archbishop of Constantinople, objected to the term Theotokos (“God-bearer/Mother of God”) for Mary, preferring Christotokos (“Christ-bearer”) — arguing that Mary bore the human nature of Christ, not the divine Logos as such. His opponent Cyril of Alexandria attacked this as dividing Christ into two persons. Condemned at the Council of Ephesus (431 AD) before all his supporters arrived, Nestorius was exiled; his followers fled to the Persian Empire. The “Nestorian” Church of the East became one of the most remarkable missionary movements in history: by 635 AD it had reached China (the Xi’an Stele records a Christian community under the Tang dynasty); it established communities throughout Central Asia, India (the Thomas Christians of Kerala have complex connections to this tradition), and Arabia. At its peak (~1000 AD) the Church of the East had more Christians under its jurisdiction than Rome and Constantinople combined. The Mongol devastations of the 13th century and Tamerlane’s genocidal campaigns (~1400 AD) nearly destroyed it. Modern scholarship questions whether Nestorius actually taught what he was condemned for — his discovered defense (The Bazaar of Heraclides) shows a position closer to Chalcedonian orthodoxy than the condemnation implies, suggesting the controversy was as much political (Cyril vs Constantinople) as theological.