Nestorius in the context of "Council of Chalcedon"

Cyril of Alexandria (Ancient Greek: Κύριλλος Ἀλεξανδρείας; Coptic: Ⲡⲁⲡⲁ Ⲕⲩⲣⲓⲗⲗⲟⲩ ⲁ̅ or Coptic: Ⲡⲓⲁⲅⲓⲟⲥ Ⲁⲃⲃⲁ Ⲕⲩⲣⲓⲗⲗⲟⲥ ⲡⲓⲥⲧⲩⲗⲗⲟⲥ ⲛ̀ⲧⲉ ⲡⲓⲛⲁϩϯ or ⲡⲓ̀ⲁⲅⲓⲟⲥ Ⲕⲓⲣⲓⲗⲗⲟⲥ; c. 376–444) was the Patriarch of Alexandria from 412 to 444. He was enthroned when the city was at the height of its influence and power within the Roman Empire. Cyril wrote extensively and was a major player in the Christological controversies of the late 4th and 5th centuries. He was a central figure in the Council of Ephesus in 431, which led to the deposition of Nestorius as Patriarch of Constantinople.

Cyril is counted among the Church Fathers and also as a Doctor of the Church, and his reputation within the Christian world has resulted in his titles Pillar of Faith and Seal of all the Fathers. The Nestorian bishops at their synod at the Council of Ephesus declared him a heretic, labelling him as a "monster, born and educated for the destruction of the church".

The Council of Ephesus was a council of Christian bishops convened in Ephesus (near present-day Selçuk in Turkey) in AD 431 by the Roman Emperor Theodosius II. This third ecumenical council, an effort to attain consensus in the church through an assembly representing all of Christendom, confirmed the original Nicene Creed, and condemned the teachings of Nestorius, Patriarch of Constantinople, who preferred that the Virgin Mary be called Christotokos, "Christ-bearer" over Theotokos, "God-bearer"; in contrast to Cyril of Alexandria who deemed that Theotokos is enough on its own. It met from 22 June to 31 July 431 at the Church of Mary in Ephesus in Anatolia.

In the 5th century in Christianity, there were many developments which led to further fracturing of the State church of the Roman Empire. Emperor Theodosius II called two synods in Ephesus, one in 431 and one in 449, that addressed the teachings of Patriarch of Constantinople Nestorius and similar teachings. Nestorius had taught that Christ's divine and human nature were distinct persons, and hence Mary was the mother of Christ but not the mother of God. The Council rejected Nestorius' view causing many churches, centered on the School of Edessa, to a Nestorian break with the imperial church. Persecuted within the Roman Empire, many Nestorians fled to Persia and joined the Sassanid Church (the future Church of the East) thereby making it a center of Nestorianism. By the end of the 5th century, the global Christian population was estimated at 10-11 million. In 451 the Council of Chalcedon was held to clarify the issue further. The council ultimately stated that Christ's divine and human nature were separate but both part of a single entity, a viewpoint rejected by many churches who called themselves miaphysites. The resulting schism created a communion of churches, including the Armenian, Syrian, and Egyptian churches, that is today known as Oriental Orthodoxy. In spite of these schisms, however, the imperial church still came to represent the majority of Christians within the Roman Empire.

At the end of the 4th century the Roman Empire had effectively split into two states although its economy and the Church were still strongly tied. The two halves of the empire had always had cultural differences, in particular exemplified by the widespread use of the Greek language in the Eastern Empire and the more limited use of Greek in the West (Greek was used in the West but Latin was displacing it as the spoken vernacular. By the 5th century scholars in the West had begun to abandon Greek in favor of the use of Latin. The Church in Rome, in particular, began to encourage the use of Latin in the western provinces and published Jerome's Vulgate, the first authorized translation of the Bible in Latin.

Nestorianism is a term used in Christian theology and Church history to refer to several mutually related but doctrinally distinct sets of teachings that fall under the umbrella term Dyophysitism, such as two natures in Christ (human and Divine) or two persons in Christ (the Man and the Word). The extent to which those two definitions are actually distinct is also debatable. The first meaning of the term is related to the teachings of Christian theologian Nestorius (d. c. AD 451) as according to his immediate opponents at the Council of Ephesus and traditionally used by Miaphysites. The second meaning of the term relates to a set of later theological teachings that were traditionally labeled as Nestorian by Chalcedonians but differ in the teachings of Nestorius in origin, scope and terminology. Per the latter definition, the Oxford English Dictionary defines Nestorianism as:

The original definition of Nestorianism, as articulated by Nestorius himself, is preserved primarily in his surviving writings on topics such as Mariology and Christology. Although many of his works were lost or destroyed, others have been transmitted through his opponents or preserved in Church of the East libraries. Most notable among these is the Bazaar of Heracleides, composed during his exile following the Council of Chalcedon. The modern rediscovery of the Bazaar has prompted renewed scholarly interest in reconstructing Nestorius’s own theological positions, which appear to diverge in significant respects from the “two‐person” formulation of Christology attributed to him by both his contemporaries and later critics. His theology was influenced by teachings of Theodore of Mopsuestia (d. 428), the most prominent theologian of the Antiochian School. Nestorian Mariology prefers the title Christotokos, which encompasses the term Theotokos ('God-bearer') for Mary, thus emphasizing distinction between divine and human aspects of the Incarnation, and at the same time their unity in the person of Christ. Nestorian Christology promotes the concept of a prosopic union of two concrete realities (divine and human) in Jesus Christ, as opposed to the concept of a hypostatic union of two hypostases into one. The distinction is between 'two hypostases in one person' and 'two hypostases united into one hypostasis', respectively. Hypostasis is not seen as subject, but rather a nature existing in reality. This Christological position is viewed by the West as radical dyophysitism, and, according to Chalcedonian Christianity, differs from their dyophysitism, which was reaffirmed at the Council of Chalcedon in 451. Such teachings brought Nestorius into conflict with other prominent church leaders, most notably Cyril of Alexandria, who issued 12 anathemas against him in 430. Nestorius and his teachings were eventually condemned as heretical at the Council of Ephesus in 431, and again at the Council of Chalcedon in 451. His teachings were considered as heretical not only in Chalcedonian Christianity, but even more so in Oriental Orthodoxy. The Church of the East would affirm the orthodoxy of Nestorius, lining up with the tradition of the School of Antioch of its time.

Eutyches (Ancient Greek: Εὐτυχής; c. 375–454) or Eutyches of Constantinople was a presbyter and archimandrite at Constantinople. He first came to notice in 431 at the First Council of Ephesus, for his vehement opposition to the teachings of Nestorius. Eutyches was condemned for having adopted a polar opposite view of Nestorianism, where the two natures (Greek: hypostases) of Christ fuse together to form one, single Divine nature, dubbed Monophysitism. This was condemned at the Council of Chalcedon and Third Council of Ephesus. He himself, however, would reject this interpretation of his thought.

The Nestorian schism (a.d. 431–544) was a split between the Christian churches of Sassanid Persia, which affiliated with Nestorius, and those that later became the Catholic and Orthodox churches. The schism rose out of a Christological dispute, notably involving Cyril (Patriarch of Alexandria) and Nestorius (Patriarch of Constantinople).

The First Council of Ephesus in 431 and the Council of Chalcedon in 451 condemned Nestorius and his doctrine, which emphasized the radical distinctness between Christ's human and divine natures. That forced a breach between the churches that defended Nestorius and the state church of the Roman Empire, which caused the Church of the East, the Christian church of Sassanid Persia, to become known as the Nestorian Church, as it took the side of Nestorius.

Theodoret of Cyrus or Cyrrhus (Ancient Greek: Θεοδώρητος Κύρρου; c. 393 – c. 458) was a notable theologian of the School of Antioch, biblical commentator, and bishop of Cyrrhus (423–457). He participated in several 5th-century Christological controversies within the Eastern Roman Church that resulted in various ecumenical acts and schisms. Theodoret wrote against Cyril of Alexandria's Twelve Anathemas, which were sent to Nestorius, and did not condemn Nestorius until the Council of Chalcedon. Selected writings by Theodoret directed against Cyril formed part of the subject matter of the Three Chapters Controversy and were condemned posthumously at the Second Council of Constantinople (533). He is accorded the epithet "Blessed" in the Eastern Orthodox Church.