The Council of Ephesus was held in Ephesus, Asia Minor in 431 under Emperor Theodosius II, grandson of Theodosius the Great. Approximately 200 Bishops were present. It was the Third Ecumenical Council. It was chiefly concerned with Nestorianism.
According to the Council, Nestorianism overemphasized the human nature of Jesus Christ at the expense of the divine. The Council denounced Patriarch Nestorius' teaching as erroneous. Nestorius asserted that Jesus Christ is one person, not two separate "people": the Man, Jesus Christ and the Son of God, Logos. The Council decreed that Lord Jesus Christ, the Son of God (Logos), is complete God and complete man, with a rational soul and body. The Virgin Mary is "Theotokos" because she gave birth not to man but to God who became man. The union of the two natures of Christ took place in such a fashion that one did not disturb the other.
The Council also declared the text of the Nicene Creed decreed at the First and Second Ecumenical Councils to be complete and forbade any additional change (addition or deletion) to it.