Nestorius' doctrine, Nestorianism, which emphasized the distinction between Christ's human and divine natures and argued that Mary should be called Christotokos (Christ-bearer) but not Theotokos (God-bearer), had brought him into conflict with other church leaders, most notably Cyril, Patriarch of Alexandria. Nestorius himself had requested the Emperor to convene the council, hoping that it would prove his orthodoxy; the council in fact condemned his teachings as heresy. The council declared Mary as Theotokos (God-bearer).
Nestorius' dispute with Cyril had led the latter to seek validation from Pope Celestine I, who authorized Cyril to request that Nestorius recant his position or face excommunication. Nestorius pleaded with the Eastern Roman Emperor Theodosius II to call a council in which all grievances could be aired, hoping that he would be vindicated and Cyril condemned.
Approximately 250 bishops were present. The proceedings were conducted in a heated atmosphere of confrontation and recriminations and created severe tensions between Cyril and Theodosius II. Nestorius was decisively outplayed by Cyril and removed from his see, and his teachings were officially anathematized. This precipitated the Nestorian Schism, by which churches supportive of Nestorius, especially in the Persian Empire of the Sassanids, were severed from the rest of Christendom and became known as Nestorian Christianity, or the Church of the East, whose present-day representatives are the Assyrian Church of the East, the Ancient Church of the East, the Chaldean Syrian Church, and the Chaldean Catholic Church. Nestorius himself retired to a monastery, always asserting his orthodoxy.