After the death of the Emperor Theodosius II in 450, his sister Pulcheria married Marcian, who accordingly became emperor. The new imperial officials convoked a council at Chalcedon in order to see to the matters of the Eutychians and the Nestorians. As a result of this council, the Coptic patriarch Dioscorus was deposed and exiled to Gangra. The council also adopted the famous Canon 28, which considered the Church of Constantinople as the “New Rome” and hence held first place among the apostolic sees. The council adopted the Tome (letter) of Leo to Flavian as orthodox.
The Coptic Church refused to recognize this council, and this caused a schism between the Orientals and the rest of Christendom. In the 20th century, theologians from the East and the West accepted that both the Chalcedonian and the non-Chalcedonian statements on Christology are acceptable as orthodox.