Second Council of Ephesus

The Second Council of Ephesus (commonly known as the Robber 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, but because of the scandalous nature of the proceedings, canon legalities, and the heterodox nature of the canons and decrees as viewed by the orthodox bishops of East and West (and the later ecumenical councils), it was never accepted as ecumenical. It was explicitly repudiated by the fourth and next ecumenical council, the Council of Chalcedon of 451, and named the Latrocinium, or "Robber Council".

The Council of Chalcedon gave rise to what has been called the Monophysite Schism between those who accepted the Second Council of Ephesus and those who accepted the Council of Chalcedon: many Byzantine emperors over the next several hundred years attempted to reconcile the opposed parties, in the process giving rise to several other schisms and teachings later condemned as heresy, such as monoenergism and monotheletism, which were devised as attempted compromises between the Chalcedonian and non-Chalcedonian parties (cf. the Henotikon and the Three Chapters - the latter itself leading to another schism lasting over a century, the Schism of the Three Chapters).

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 that in Christ there exists one united nature [miaphysis], that of a divine human. 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".