Council of Ephesus: third of the seven Ecumenical Councils in which Christian doctrine was established (431).
- Organized by the emperor Theodosius II;
- discussion of the teachings of bishop of Nestorius of Constantinople, who belonged to the Antiochene school of theology; Nestorius recognized that in Christ man and God were united, but he saw this as a psychological unity, whereas the Alexandrine and Roman theologians, led by Cyril of Alexandria, argued for a more physical unity;
- the council started before the Antiochenes could arrive and condemned Nestorianism;
- the Antiochenes organized a council of their own, which accepted Nestorius' teachings;
- the emperor recognized the first council as orthodox, and this decision was confirmed by pope Coelestinus I;
- as a result, the theologians of Alexandria, Constantinople, and Rome decided that he Blessed Virgin should not be called Christotokos ("Mother of Christ") but Theotokos ("Mother of God").
- the Antiochene theologians never accepted this outcome; they settled in the Sasanian Empire, where their christology was established in the Councils of Bet-Lapat (484) and Seleucia (486) ("Nestorian" or "Assyrian Church");
- although it was by now agreed by many theologians that in Christ two natures were united, it remained unclear how.