The Gregorian reform movement contributed to dissatisfaction with the church among townspeople as well as monarchs. Papal moves against simony, for example, led to widespread concern about the role of money in the church. Papal efforts to improve the sexual morality of the clergy led some laypersons to assume they could, and indeed should, remove priests for any type of immorality.

Criticism of the church emerged in many places but found its largest audience in the cities, where the contrast between wealth and poverty could be seen more acutely. In northern Italian towns, the monk Arnold of Brescia (BREH-shah) (ca. 1090–1155) denounced clerical wealth. In France, Peter Waldo (ca. 1140–ca. 1218), a rich merchant of the city of Lyons, gave his money to the poor and preached that only prayers, not sacraments, were needed for salvation. The Waldensians (wawl-DEHN-shuhnz) — as Peter’s followers were called — bitterly attacked the sacraments and church hierarchy, and they carried these ideas across Europe. In the towns and cities of southern France, the Albigensians (al-buh-JEHN-see-uhns), also known as the Cathars, used the teachings of Jesus about the evils of material goods to call for the church to give up its property. People who rejected worldly things, not wealthy bishops or the papacy, should be the religious leaders.

Critical of the clergy and spiritually unfulfilled, townspeople joined the Waldensians and the Albigensians. The papacy denounced supporters of both movements as heretics and began extensive campaigns to wipe them out. In 1208, Pope Innocent III proclaimed a crusade against the Albigensians, and the French monarchy and northern French knights willingly joined in, eager to gain the lands and wealth of southern French cities. After years of fighting, the leaders agreed to terms of peace, which left the French monarchy the primary beneficiary. Later popes sent inquisitors with the power to seek out and eliminate the remaining heretics.