1208 CE, c. March
Pope Innocent III issues a papal bull calling for the Albigensian Crusade against the Cathar heretics in southern France, c. March 14, 1208, after a papal legate, Pierre de Castelnau, was assassinated. Pope Innocent III, offered indulgences (forgiveness for sins) to participants and promised the lands of the heretics to any noble who would fight.
The Albigensian Crusade did not officially begin until the following year, when the crusader army assembled in Lyon in southern France in the summer of 1209 and went on to commit the "Massacre at Béziers" on July 22, 1209. Where the Crusaders sacked the city, slaughter thousands of inhabitants, both Cathars and Catholics, and burned the city to the ground. The event is associated with the phrase, "Kill them all; God will know his own," allegedly uttered by papal legate Arnaud Amalric.
The military Albigensian campaign continued for 20 years until1229. But shifted after the Béziers massacre, to more of an Inquisition led "search and punish campaign" to root out remaining Cathar "heretics". It technically ended on April 12, 1229, with the signing of the Treaty of Paris (Treaty of Meaux), which secured French royal control over Languedoc. However resistance continued until 1244 with the fall of Montségur, and the final Cathar stronghold of Quéribus fell in 1255, following years of Inquisition, about 45 years after it started.
