Fourth Ecumenical Council: Chalcedon (451)

Defined the two natures of Christ, divine and human, in one Person, "without confusion, without change, without division, without separation." Condemned the one-nature teaching of Eutyches. Canon 28 gave the see of Constantinople privileges equal to those of older Rome while ranking it second in order after her; Rome refused to ratify that canon, though it received the definition of faith. 630 bishops attended, the largest of the ancient councils.