Because the Cathars denied the power of Catholic sacraments and priests, refused to pay tithes or other church taxes, and preached against the corruption of the Catholic Church, the Cathars posed a threat to the power of the Pope and the Catholic Church. The fact that the local secular lords tolerated the heretics in their territories was a further provocation to Rome – and this provided an excuse for the Kings of France to impose their sovereignty over a region that was effectively independent of the Crown at the start of the 11th century.
In 1208, Pope Innocent III called for a “crusade” against the Cathars, or Albigensians. The Pope offered to the knights, noblemen, and mercenaries who took part in this crusade the same forgiveness of sins and cancellation of debts that he offered crusaders against the Saracens in the Holy Land. The following year, in 1209, a crusading army descended on the Languedoc and massacred the inhabitants of the city of Béziers. Allegedly some 20,000 people were put to the sword, including those seeking refuge in the cathedral and the Catholic priests with them.
The most intransigent of the local barons, Raymond-Roger de Trencavel, Viscount of Béziers and Carcassonne, was forced to capitulate. After a long siege of his the fortress-city of Carcassonne, he surrendered his own person to save the lives of the city’s residents and defenders. His lands were given to one of the leaders of the crusade, Simon de Montfort. Raymond-Roger was confined to his own dungeon, where he died three months later. Although the crusaders returned home, Simon de Montfort remained in the Languedoc to try to subdue his unruly vassals, and a long, drawn-out war ensued, characterized by merciless sieges, atrocities, and assassinations.
Meanwhile, a brilliant Cistercian scholar, Dominic Guzman, challenged the Cathars on their own ground, debating with the Cathar preachers and, like them, living a life of humility and poverty. He founded a new preaching order, the Dominicans, whose goal was to fight the heresy by reason and example.
But converting people one by one was a slow process. Neither the Popes in Rome nor the Kings of France were content to wait for the Dominicans to succeed. A second Albigensian Crusade was launched in 1226. In the course of half a century, a combination of armed force and the judicial intimidation by the newly formed Inquisition slowly eradicated the heresy and broke the opposition of the local nobility.