Council of Chalcedon

The Council of Chalcedon was a church council held from October 8 to November 1, 451 AD, at Chalcedon (a city of Bithynia in Asia Minor), on the Asian side of the Bosporus, known in modern times as Istanbul. The council marked a significant turning point in the Christological debates that led to the separation of the church of the Western Roman Empire in the 5th century. It is the last council which many Anglicans and most Protestants consider ecumenical.

The Council of Chalcedon was convened by Emperor Marcian, with the reluctant approval of Pope Leo the Great, to set aside the 449 Second Council of Ephesus, better known as the "Robber Council". The Council of Chalcedon issued the 'Chalcedonian Definition,' which repudiated the notion of a single nature in Christ, and defined that he has two natures in one person and hypostasis; it also insisted on the completeness of his two natures: Godhead and manhood. The council also issued 27 disciplinary canons governing church administration and authority. In a further decree, later known as the canon 28, the bishops declared the See of Constantinople (New Rome) equal in honor and authority to Rome.

The Council is considered by the Roman Catholics, Eastern Catholic Churches, the Eastern Orthodox Church, the Old Catholics, and various other Western Christian groups to have been the Fourth Ecumenical Council. As such, it is recognized as infallible in its dogmatic definitions by the Roman Catholic and Eastern Orthodox Churches (then one church). Most Protestants also consider the concepts of the Trinity and Incarnation as defined at Nicaea (in 325) and Chalcedon to be orthodox doctrine to which they adhere. However, the Council is not accepted by several of the ancient eastern churches, including the Oriental Orthodox of Egypt, Syria and Armenia, and the Assyrian Church of the East. The Oriental Orthodox teach 'one nature' in Christ, composed of both Godhead and manhood. Misrepresented as a denial of his true humanity, this used to be denigrated as the heresy of Monophysitism, though now the neutral terms Miaphysite and Miaphysitism are widely preferred.