The Council of Chalcedon (kælˈsiːdən,_ˈkælsɪdɒn; Concilium Chalcedonense) was the fourth ecumenical council of the Christian Church. It was convoked by the Roman emperor Marcian. The council convened in the city of Chalcedon, Bithynia (modern-day Kadıköy, Istanbul, Turkey) from 8 October to 1 November 451 AD. The council was attended by over 520 bishops or their representatives, making it the largest and best-documented of the first seven ecumenical councils. The principal purpose of the council was to re-assert the teachings of the ecumenical Council of Ephesus against the heresies of Eutyches and Nestorius. Such heresies attempted to dismantle and separate Christ's divine nature from his humanity (Nestorianism) and further, to limit Christ as solely divine in nature (Monophysitism).
As recorded by American Christian scholar Jaroslav Pelikan, it was stated:We all teach harmoniously [that he is] the same perfect in godhead, the same perfect in manhood, truly God and truly man, the same of a reasonable soul and body; homoousios with the Father in godhead, and the same homoousios with us in manhood ... acknowledged in two natures without confusion, without change, without division, without separation.
Whilst this judgment marked a significant turning point in the Christological debates, it also generated heated disagreements between the council and the Oriental Orthodox Church, who did not agree with such conduct or proceedings. This disagreement would later inform the separation of the Oriental Orthodox Churches from the rest of Christianity, and led to the council being regarded as "Chalcedon, the Ominous".
The council's other responsibilities included addressing controversy, dealing with issues such as ecclesiastical discipline and jurisdiction, and approving Statements of Belief such as the Creed of Nicaea (325), the Creed of Constantinople (381 subsequently known as the Nicene Creed), two letters of St. Cyril of Alexandria against Nestorius, and the Tome of Pope Leo.