Chalcedon, a city of ancient Bithynia, at the entrance of the Euxine, opposite to Byzantium. It was founded 684 B.C. by a colony from Megara, and soon became a place of considerable trade and importance. Taken by the Persians, it finally merged into the Roman empire, under which it was made a free city. Chosroes, the Persian, captured it in 616 A.D., after which it declined, until it was finally demolished by the Turks, who used its ruins to build mosques and other edifices at Constantinople. Chalcedon was the birthplace of the philosopher Xenocrates.
The council of Chalcedon was the fourth œcumenical council, and was assembled (451 A.D.) by the emperor Marcian for the purpose of drawing up a form of doctrine in regard to the nature of Christ which should equally avoid the errors of the Nestorians (q.v.) and Monophysites (q.v.). Six hundred bishops, almost all of the Eastern Church, were present. The doctrine declared to be orthodox was, that in Christ there were two natures, which could not be intermixed (this clause was directed against the Monophysites), and which also were not in entire separation (this was directed against the Nestorians), but which were so conjoined, that their union destroyed neither the peculiarity of each nature, nor the oneness of Christ's person.