Nestorius

Nestorius of Constantinople (Ancient Greek: Νεστόριος; Syriac: ܡܪܝ ܢܣܛܘܪܝܣ, Mār Nesṭōrīs; c. 386 – c. 451) was an early Christian prelate who served as Archbishop of Constantinople from 10 April 428 to 11 July 431. He was a Christian theologian from the Catechetical School of Antioch, and several of his teachings in the fields of Christology and Mariology were seen as controversial and heretical, causing major disputes.

In 431, he was condemned and deposed from his see by the Council of Ephesus, presided over by his archrival Cyril of Alexandria, but the counter-council led by John I of Antioch vindicated him and deposed Cyril in return. Nestorius refrained from attending both of these councils and instead sought retirement from the Byzantine Emperor.

Nestorius himself used the title Theotokos and did not advocate for its ban. His teachings included cautious usage of Theotokos ("God-Bearer"), used for Mary, mother of Jesus, in order that Christ's human and divine natures not be confused, as he believed Christ was born according to his humanity and not his divinity, which indicated his preference for the concept of the prosopic union of two natures (divine and human) of Christ, over the later concept of a hypostatic union. He proposed instead the title of Christotokos ("Christ-bearer"). This brought him into conflict with Cyril of Alexandria and other prominent miaphysite churchmen of the time, who accused him of heresy.

If the babe and the Lord of the babe are one and the same person, the suspected phrase "inhabitant of the babe" must be simply intended as a safeguard against identification of the Word with the flesh. So Mary is Theotokos – because the Word was united to the temple ... which is in nature consubstantial with the holy Virgin ... It is in virtue of this union that the holy Virgin is called Theotokos

Nestorius sought to defend himself at the Council of Ephesus in 431, but instead found himself formally condemned for heresy by a majority of the bishops and was subsequently removed from his see. On his own request, he retired to his former monastery, in or near Antioch. In 435, Theodosius II sent him into exile in Upper Egypt, where he lived on until about 451, strenuously defending his views. His last major defender within the Roman Empire, Theodoret of Cyrrhus, finally agreed to anathematize him in 451 during the Council of Chalcedon.