An ecumenical council, the first Council of Ephesus was convened, under Emperor Theodosius II, in A.D. 431 and held in Ephesus (modern Turkey) to discuss the position of Nestorius on the dual or singular nature of Jesus Christ. Nestorianism was condemned. Monophysitism, which opposed Nestorianism, was not accepted at this council, although it was at the second Council of Ephesus in 449 and then rejected at the Council of Chalcedon in 451. Mary was declared Theotokos (mother of God).
References:
A World Without Islam
Ancient Rome: a Military and Political History, by Christopher S. Mackay
History of the development of the doctrine of the person of Christ, tr. by W.L. Alexander and D.W. Simon
[www.piar.hu/councils/ecum03.htm#Twelve%20Anathemas%20Proposed%20by%20Cyril%20and%20accepted%20by%20the%20Council%20of%20Ephesus] Documents From the 1st Council of Ephesus
