Leo I, Saint (Saint Leo the Great), c.400-461, pope (440-61), an Italian; successor of St. Sixtus III. A Doctor of the Church, he was one of the greatest pontiffs of the early years of the church. He waged a firm campaign against schism and heresy. With the aid of Valentinian III, the Roman emperor of the West, he campaigned to eliminate Manichaeism from Italy. Later, asserting his authority over St. Hilary of Arles, he obtained an imperial rescript that effectively confirmed the authority of the pope over all his bishops. In the Nestorian-Monophysite controversy Leo was the leader in defending Catholic teaching. He wrote the celebrated Tome of Leo, a doctrinal letter defining the two natures and one person of Christ that was later adopted as ecumenical at Chalcedon (see Chalcedon, Council of), when the heresiarch Eutyches was condemned. He was also effective as a statesman and met (452) Attila the Hun to persuade him not to invade Rome. In 455 he similarly urged Gaiseric the Vandal to spare the lives of the Romans. St. Leo's letters and sermons reflect the many aspects of his career and personality, including his great personal influence for good, and are invaluable historical sources. His rhythmic prose style, called cursus leonicus, influenced ecclesiastical language for centuries. The celebrated Leonian Sacramentary, the oldest form of the Roman Missal, is probably not his work. He was succeeded by St. Hilary. Feast: Apr. 11.

Leo I, d. 474, Byzantine or East Roman emperor (457-74). Chosen by the senate to succeed Marcian, he sought to counteract the preponderance of Germans in the Roman army by enlisting Isaurians. A naval expedition (468) against the Vandals of Africa failed through the incompetence or treachery of the commander, Basiliscus, who delayed his attack until Gaiseric was able to attack him with fire ships. Leo I was succeeded by his grandson, Leo II, a child of six, who died in the year of his accession; Leo I's son-in-law, Zeno, then became emperor.

known as Leo the Great

(born 4th century, Tuscany?—died Nov. 10, 461, Rome; Western feast day November 10, Eastern feast day February 18) Pope (440–461). He was a champion of orthodoxy and a Doctor of the Church. When the monk Eutyches of Constantinople asserted that Jesus Christ had only a single divine nature, Leo wrote the Tome, which established the coexistence of Christ's human and divine natures. Leo's teachings were embraced by the Council of Chalcedon (451), which also accepted his teaching as the “voice of Peter.” Leo dealt capably with the invasions of barbaric tribes, persuading the Huns not to attack Rome (452) and the Vandals not to sack the city (455). Leo was also an exponent of the precept of papal primacy, and his personal example and letters and sermons contributed greatly to the growth of papal authority.

Learn more about Leo I, Saint with a free trial on Britannica.com.

known as Leo the Great

(born 4th century, Tuscany?—died Nov. 10, 461, Rome; Western feast day November 10, Eastern feast day February 18) Pope (440–461). He was a champion of orthodoxy and a Doctor of the Church. When the monk Eutyches of Constantinople asserted that Jesus Christ had only a single divine nature, Leo wrote the Tome, which established the coexistence of Christ's human and divine natures. Leo's teachings were embraced by the Council of Chalcedon (451), which also accepted his teaching as the “voice of Peter.” Leo dealt capably with the invasions of barbaric tribes, persuading the Huns not to attack Rome (452) and the Vandals not to sack the city (455). Leo was also an exponent of the precept of papal primacy, and his personal example and letters and sermons contributed greatly to the growth of papal authority.

Learn more about Leo I, Saint with a free trial on Britannica.com.