The Second Council of Ephesus was a Christological church synod in 449 AD convened by Emperor Theodosius II under the presidency of Pope Dioscorus I of Alexandria. It was intended to be an ecumenical council, and it is accepted as such by the miaphysite churches but was rejected by Chalcedonian Christians. It was explicitly repudiated by the next council, the Council of Chalcedon of 451, recognised as the fourth ecumenical council by Chalcedonian Christians, and it was named the Latrocinium ("Robber Synod") by Pope Leo I; the Chalcedonian churches, particularly the Roman Catholic and Eastern Orthodox communions, continue to accept this designation, while the Oriental Orthodox repudiate it.
Both this council and that at Chalcedon dealt primarily with Christology, the study of the nature of Christ. Both councils affirmed the doctrine of the hypostatic union and upheld the orthodox Christian doctrine that Jesus Christ is both fully God and fully man. The Second Council of Ephesus decreed the formula of Cyril of Alexandria, stating that Christ is one incarnate nature [mia physis] (a qualitative description of the union of divinity and humanity), fully human and fully God, united without separation, without confusion, without mixture and without alteration. The Council of Chalcedon decreed that in Christ two natures exist, "a divine nature [physis] and a human nature [physis], united in one person [hypostasis], with neither division nor confusion".
Those who do not accept the decrees of Chalcedon nor later ecumenical councils are variously named monophysites, miaphysites, or non-Chalcedonians, and comprise what is today known as Oriental Orthodoxy, a communion of six autocephalous ecclesial communions: Coptic Orthodox Church of Alexandria, Ethiopian Orthodox Tewahedo Church, Eritrean Orthodox Tewahedo Church, Malankara Orthodox Syrian Church, Syriac Orthodox Church, and the Armenian Apostolic Church. Those who accepted the teaching of Chalcedon but resided in areas dominated by Oriental Orthodox bishops were called by the non-Chalcedonians Melkites ("King's men"), as the Emperors were usually Chalcedonians. The Antiochian Orthodox Church historically descends from these people. Shortly after the Council of Chalcedon, the miaphysite party appointed a Pope of Alexandria in opposition to the Chalcedonian Pope of Alexandria. Over the next few centuries, various popes usually held to either one side or the other although some accepting the Henotikon. Eventually, two separate papacies were established, each claiming sole legitimacy.
Background
Nestorius was Archbishop of Constantinople. His opponents charged him with detaching Christ's divinity and humanity into two persons existing in one body, thereby denying the reality of the Incarnation. It is not clear whether Nestorius actually taught that. A combination of politics and personalities contributed to Nestorius being judged a heretic and deposed at the Council of Ephesus in 431 AD. John Anthony McGuckin sees an "innate rivalry" between the Sees of Alexandria and Constantinople.
Eutyches was an archmandrite in Constantinople. In his opposition to Nestorianism, he seemed to take an equally extreme, although opposite view. In 448, Flavian, Bishop of Constantinople held a synod at which Eusebius, Bishop of Dorylaeum, brought a charge of heresy against Eutyches. Eutyches was summoned to appear and clarify his position regarding the nature of Christ. Finding his response unsatisfactory, the synod condemned and exiled Eutyches, who sent an appeal to Pope Leo I. When Leo had received the Acts of the council, he concluded that Eutyches was a foolish old man who had erred through ignorance, and might be restored if he repented. Dioscurus of Alexandria, imitating his predecessors in assuming a primacy over Constantinople, simply annulled the sentence of Flavian, and absolved Eutyches. Dioscurus and Eutyches had obtained the convocation by the Emperor of an ecumenical council to meet at Ephesus in August, 449.
First session
The Acts by the Second Council of Ephesus are known through a Syriac translation by a monk, that was published by the British Museum (MS. Addit. 14,530) and written in 535. The first session is missing.