St. Leo the Great was born in Tuscany. As deacon, he was dispatched to Gaul as a mediator by Emperor Valentinian III. He reigned as Pope between 440 and 461. He persuaded Emperor Valentinian to recognize the primacy of the Bishop of Rome in an edict in 445. The doctrine of the Incarnation was formed by him in a letter to the Patriarch of Constantinople, who had already condemned Eutyches. At the Council of Chalcedon this same letter was confirmed as the expression of Catholic Faith concerning the Person of Christ. 

All secular historical treatises eulogize his efforts during the upheaval of the fifth century barbarian invasion. His encounter with Attila the Hun, at the very gates of Rome persuading him to turn back, remains a historical memorial to his great eloquence. When the Vandals under Genseric occupied the city of Rome, he persuaded the invaders to desist from pillaging the city and harming its inhabitants. He died in 461, leaving many letters and writings of great historical value.