When Cardinal Ratzinger was elected pope, taking the name Benedict XVI, the first words he spoke from the balcony of Saint Peter’s Basilica referred to his predecessor, Pope John Paul II, whom he referred to as “the great pope.” Since then, many have referred to him as “John Paul the Great.” Prior to that, only three popes came to be universally called “the Great”—Saint Gregory the Great (590–604), Saint Nicholas the Great (858–867), and the pope we honor today, Saint Leo the Great (440–461), who was the first pope to receive that title. Leo was born in Tuscany, within the Western Roman Empire, at a time when the empire was experiencing decline due to ongoing threats of barbarian invasions, internal administrative disputes, and a difficult economic situation. Leo considered himself a Roman, since he spent his early years in the city. While still young, he was ordained a deacon in Rome under Pope Celestine and served him and his successor, Pope Sixtus III, in this capacity from 430–439....