Aeterna Dei Sapientia §5

⁵ Leo was born toward the end of the fourth century. The Liber Pontificalis informs us that he was "of Tuscan nationality from his father Quintian." (4) Since, however, he spent his early years in Rome, he not unnaturally called this city his patria [homeland]. (5) While still a young man he joined the ranks of the Roman clergy and in due course was ordained deacon. In this capacity he rendered signal service to Pope Sixtus III between the years 430 and 439, and played a considerable part in the conduct of Church affairs. Among the many friends he made at this time were St. Prosper, bishop of Aquitania, and Cassian, founder of the celebrated Abbey of St. Victor in Marseilles. Cassian, whom he persuaded to write De Incarnatione Domini ( 6 ) against the Nestorians, proclaimed him "the glory of the Church and the sacred ministry" (7)—praise indeed for a simple deacon!