The Council of Chalcedon 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 from 8 October to 1 November 451. 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 teachings of Eutyches and Nestorius. Such doctrines viewed Christ's divine and human natures as separate (Nestorianism) or viewed Christ as solely divine (monophysitism).

Marcian was Roman emperor of the East from 450 to 457. Very little of his life before becoming emperor is known, other than that he was a domesticus who served under the commanders Ardabur and his son Aspar for fifteen years. After the death of Emperor Theodosius II on 28 July 450, Marcian was made a candidate for the throne by Aspar, who held much influence because of his military power. After a month of negotiations Pulcheria, Theodosius' sister, agreed to marry Marcian. Zeno, a military leader whose influence was similar to Aspar's, may have been involved in these negotiations, as he was given the high-ranking court title of patrician upon Marcian's accession. Marcian was elected and inaugurated on 25 August 450.