Leo, name of 13 popes. Saint Leo I (c. 400–461), an Italian, r. 440–461. Called “the Great,” he suppressed heresy and established his authority in both the West and East. He persuaded the barbarian leaders Attila (in 452) and Genseric (in 455) not to destroy Rome. Saint Leo III (d. 816), a Roman, r. 795–816. He crowned Charlemagne “Emperor of the Romans” in Rome on Christmas Day, 800, thus allying church and state. Saint Leo IX (Bruno of Egisheim; 1002–1054), a German, r. 1049–54. He fought against simony (the selling of church offices) and vigorously enjoined clerical celibacy. The Great Schism between the Western and Eastern churches began in his reign. Leo X (Giovanni de Medici; 1475–1521), a Florentine, r. 1513–21. He made Rome a center of the arts and literature and raised money for rebuilding St. Peter's by the sale of indulgences—a practice attacked by Martin Luther at the start of the Reformation. Leo XIII (Gioacchino Pecci; 1810–1903), an Italian, r. 1878–1903. He worked to reconcile Roman Catholicism with science and liberalism and generally applied Christian principles to the religious and social questions of his time. His Rerum Novarum (1891), an encyclical (letter to the Roman Catholic Church) on the condition of the working classes, strengthened Roman Catholicism's links with the working-class movement and helped counter anticlericalism at home and abroad.