Leo I, Saint (400?-461), was elected pope in 440. He was also called the Great. Leo is most famous for defending orthodox church theology and for defining papal authority.
Leo was probably born in Tuscany in northern Italy. He exercised more day-to-day power than any previous pope. He devoted much of his reign to extending his control and authority over the bishops of Italy, Gaul, Spain, and North Africa. Leo worked out the Petrine theory of papal primacy (supreme authority). This theory states that Jesus named Saint Peter as the leader among the original apostles (Matt. 16:17-19). The theory claimed that Peter’s successors, the bishops of Rome, inherited Peter’s authority. See Pope (The early papacy).
Through Leo’s work at the Council of Chalcedon in 451, basic doctrines were proclaimed about Jesus Christ, especially about His divine and human natures. These doctrines remain in force in most Christian churches today. Leo gained much respect during his reign for persuading Attila, king of the Huns, not to attack Rome in 452. Leo also worked out an agreement with Gaiseric (or Genseric), leader of the Vandal tribe, that limited the force and destructiveness of a Vandal attack on Rome in 455. He died on Nov. 10, 461.
Leo was a gifted and forceful writer, leaving 123 authentic letters and 96 sermons. He was not an original thinker, but he had a great ability to organize and explain the thought of previous popes.
