Chalcedon, Council of, fourth ecumenical council, convened in 451 by Pulcheria and Marcian, empress and emperor of the East, to settle the scandal of the Robber Synod and to discuss Eutychianism (see Eutyches). It deposed the principals in the Robber Synod and destroyed the Eutychian party. Its great work, however, was its Definition regarding the nature and person of Jesus. Based upon the formulation given by Pope St. Leo I in his famous Tome to Flavian, it declared that, contrary to the view taken by Eutychianism (see Eutyches) and Monophysitism, the second Person of the Trinity has two distinct natures—one divine and one human. It was also proclaimed that these two natures exist inseparably in one person. This difference was a major factor in the Monophysite schism that divided the East for centuries. The council produced 28 disciplinary canons important for canon law in both the East and West. However, the Roman Catholic Church did not admit the 28th canon, which made the patriarch of Constantinople second only to the pope in Rome in precedence, until the Fourth Lateran Council (1215).
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