The Third Ecumenical Council (Ephesus, 431)

Nestorius, Archbishop of Constantinople, objected to calling the Virgin Mary Theotokos (Mother of God), proposing “Christotokos” instead. St Cyril of Alexandria saw in this a division of Christ into two persons — God the Word and the man Jesus. The Emperor Theodosius II convened a council at Ephesus in 431.

Under the presidency of St Cyril the Council deposed Nestorius and confessed that the Son of God and the Son of the Virgin are one person; therefore the Virgin Mary is truly Theotokos. The seventh canon forbade composing any creed other than that of Nicaea. The Council also condemned Pelagian teaching.

The Eastern bishops led by John of Antioch, who arrived late, met separately and did not recognise the decisions. Reconciliation was reached in 433 on the basis of the so-called Formula of Reunion accepted by Cyril and John.

The title Theotokos became central to Orthodox theology and worship. The Assyrian Church of the East, which venerates Nestorius, did not accept this Council.