The development of this "heresy" means that new principles, opposite to those of medieval feudal society will be put into practice.
In 1206 Dominique de Guzman tries to preach against the Cathars. It fails. In 1208, giving the murder of his legate Pierre de Castelnau as a pretext, pope Innocentius III calls up to the crusade against the heretics.
The lords of northern France led by Arnaud Amaury, abbot of Cîteaux, take weapons. King Philippe Auguste carefully stays in Paris. In july 1209, Béziers is taken, the whole city is destroyed, the whole population is killed. Many of them are burned in Madeleine church. To a soldier who asks him how to make the difference between the Cathars and the good Catholics, Arnaud Amaury pronounces these famous words : "Kill them all, God will recognize his."
In 1215 Toulouse is invaded by the French, but the count very quickly reconquers his capital. During a second siege in june 1218 Simon de Montfort dies. He is killed by a big stone thrown at him by the women of Toulouse defending the walls.
After his death the crusaders are completely disorganized. They are chased away from Carcassonne in 1224. The French King Louis VIII has to come himself to boost their morale and a new offensive at the same time ! He gets good results, as Raimond VII new count of Toulouse has to sign the Treaty of Meaux in 1229 : he surrenders !
In 1233 pope Gregorius IX creates the Inquisition, whose task is to chase and judge the heretics.
The territorial conquest is accomplished, but the first purpose of the crusade, namely fighting catharism, is a complete failure.
The Dominicans are in charge of the Inquisition. In 1242 the two Great Inquisitors are murdered with their escort in Avignonet-Lauragais (a village between Toulouse and Carcassonne) by a troop of knights coming down from Montségur. In Montségur lives a very important community of Cathars who had settled down there, being chased away from everywhere.
This perched and strengthened village symbolizing Catharism is taken after a 9 month siege, on March, 2, 1244.
On March, 16, more than 200 heretics are burned at the stake in front of the citadel. The place is still called "Camp dels Cremats" in occitan language (the field of the burned). This stake becomes the symbol of their martyr.
Quéribus castle, situated in the Corbières area, is the last bastion of Catharism, and it is taken only in 1255.
The King of France Saint Louis immediatelly takes over the region. Carcassonne's citadel is considerably strengthened.
The county of Toulouse is annexed to the French Kingdom in 1271, when Jeanne, last daughter of the last count and her husband Alphonse, brother of King Saint Louis die without children. A complicated history, isn't it ??