909–1122

The Cluniac and Gregorian Reform: the Investiture Controversy from Canossa to the Concordat of Worms

In 909/910 Duke William of Aquitaine founded the monastery of Cluny, shielded from interference by bishops and lords. A succession of its abbots inspired a reform of the whole Church. The reform was against simony and for clerical celibacy and obedience to the pope.

In the 9th–10th centuries the papacy was in deep moral decline: the "pornocracy," the trial of the corpse of Pope Formosus in 897. Against this background the reform, backed by Emperor Henry III, led to the papacy of Leo IX (1049–1054). In 1059 the right to elect the pope passed to the college of cardinals.

The reform peaked under Gregory VII (Hildebrand, 1073–1085). He fought simony and clerical marriage, and then imperial investiture of bishops. He issued the "Dictatus Papae" on papal supremacy.

Conflict with Emperor Henry IV led to the emperor's excommunication. In January 1077 came his penitential "walk to Canossa." A second excommunication followed later, and Gregory VII was expelled from Rome. He died in 1085.

The dispute ended in compromise: the Concordat of London (1107) and the Concordat of Worms (1122). They divided bishops' spiritual and temporal investiture between church and ruler.