Pope (440–61). He established the authority of the papacy by defending orthodoxy in regions far distant from his authority in Italy, most notably in Spain, Gaul, Africa, and the East. The Pelagian and Manichean sects in particular threatened papal control and authority. At Chalcedon in 451 he obtained agreement between Eastern and Western churches on defining for Christian believers the relationship of God the Father to the Son. The following year he persuaded the barbarian Attila to leave Italy. In 455 he saved Rome from Vandal destruction.