The First Council at Ephesus in 431 A.D. formally condemned Nestorius‘ view as heresy. Cyril of Alexandria was very concerned for the questioned raised by Nestorius and accused Nestorius publicly in the council. Cyril appealed to Celestine of Rome, Church Father who held papal authority from 422 to 432 to excommunicate Nestorius for his lowly view of Christ’s divine and human nature. The Emperor Theodosius II (401–450) called for the Third Ecumenical Council to decide on veneration of Virgin Mary who was titled as the “Mother of God“. Delegates from the Eastern and Western churches came to the council. For some reason, delegates from the East were late to arrive in the council. So, Cyril conducted the council in the absence of Nestorius and condemned him and his teaching in his absence.
John I of Antioch learned upon his arrival to the council that Nestorius had been already condemned. Now, Nestorius in support of John I of Antioch held their own synod that condemned and deposed Cyril and the previous council in Ephesus. Later, both sides were deposed and exiled by the emperor. Afterwards, West came along and condemned Nestorius the heretic.