431–433

Cyril of Alexandria, the Council of Ephesus (431) and the Formula of Union (433)

Against the "dividing" christology of Nestorius, Cyril taught that Christ is not a man in whom God dwelt but God the Word become flesh: the divine and the human are united "hypostatically", the Lord's humanity has no hypostasis of its own and exists in the Word, and therefore Mary is Theotokos. In the Second Letter (early 430) he asks Nestorius to rely on the Nicene Creed, and in the Third Letter he demands that Nestorius accept twelve anathemas; Nestorius refused. In 431 Theodosius II convened a council at Ephesus; Cyril opened it before the Antiochenes arrived, Nestorius was condemned and deposed, the Second Letter was approved as a document of the ecumenical faith, and Mary was proclaimed Theotokos. The Antiochenes, arriving under John of Antioch, held their own council and deposed Cyril, while the Roman legates supported Cyril. In 433 the sides were reconciled: Cyril accepted a moderate Antiochene document – the Formula of Union (Christ is perfect God and perfect man, consubstantial with the Father in Godhead and with us in humanity, a "union of two natures", Mary is Theotokos), and the Antiochenes agreed to the deposition of Nestorius.