Pope from 514. His chief importance lies in his healing of the Acacian schism. In 519 he secured the signature of John, Patr. of Constantinople, and afterwards of some 250 E. bishops, to a dogmatic formula in which the Chalcedonian Definition and Leo's Tome were accepted, Acacius and other heretics condemned, and the authority of the Roman see emphasized. Feast day, 6 Aug.