The Cathars were especially numerous in southern France, in the region of Languedoc, then part of the Catalan-Aragonese Confederation or Kingdom of Aragon. They were termed Albigensians because of the movement's presence in and around the city of Albi. Political control in Languedoc was split amongst many local lords and town councils, the area was relatively lightly oppressed and reasonably advanced.
The crusading efforts can be divided into a number of periods, the first from 1209 to 1215 was a series of great success for the crusaders in Languedoc. The captured lands however were largely lost between 1215 and 1225 in a series of revolts and reverses. The situation turned again following the intervention of the French king, Louis VIII, in 1226. He died in November of that year, but the efforts continued under Louis IX; the area was reconquered by 1229 and main protagonists made peace. From 1233 the efforts of the Inquisition to crush Catharism were key, there was resistance and revolts with the military action finally ending in 1255 but the Cathar efforts were clearly doomed.
Pope Innocent III organised the vigorous supression of the Cathars. He sent a papal legate to investigate Languedoc in 1204 and found that it would be difficult to convert the heretics. The Pope called upon the French king, Philippe II, to act against those nobles who permitted Catharism, but Philippe was involved in the Bouvines War and declined to act. In 1206 the Pope sought support for action from the nobles of Languedoc. The powerful count Raymond VI of Toulouse refused to assist and was excommunicated in May, 1207. Raymond met with a papal representative, Pierre de Castelnau, in January 1208, and after an angry meeting Pierre de Castelnau was killed the following day. The Pope reacted to the affront by a bull declaring a crusade against Languedoc — offering the land of the heretics to any who would fight.
By mid 1209 around 10,000 crusaders had gathered in Lyon and began to march south. In June Raymond of Toulouse, recognizing the potential disaster at hand, promised to act against the Cathars, and his excommunication was lifted. The crusaders headed towards Montpellier and the lands of Raymond-Roger de Trencavel, aiming for the Cathar communities around Albi and Carcassonne. Like Raymond of Toulouse, Raymond-Roger de Trencavel sought an accommodation with the crusaders, but Raymond-Roger was refused a meeting and raced back to Carcassonne to prepare his defences.
In July the crusaders captured the small village of Servian and headed for Béziers, arriving on July 21. They surrounded the town and demanded the Catharists be handed over; the demand was refused. The town fell the following day, an abortive sortie was pursued back into the town and the population was slaughtered. According to Caesar of Heisterbach the papal representative, Abbot Arnaud-Amaury, declared "Caedite eos! Novit enim Dominus qui sunt eius" — Latin for "Slay them all! God will know his own." Béziers is believed to have held no more than 500 Cathars, but over 10,000 citizens were killed. The news of the horror at Béziers quickly spread and many settlements were cowed.
The next major target for the crusade was Carcassonne. The town was well fortified, but vulnerable and over-populated with refugees. The crusaders arrived outside the town on August 1, 1209. The siege did not last long, by August 7 the crusaders had cut the town's access to water, Raymond-Roger sought negotiations but was taken prisoner while under truce, and the town surrendered on August 15. The inhabitants were not massacred but all were forced to leave the town. The crusader Simon de Montfort was granted control of the area encompassing Carcassonne, Albi, and Béziers. After Carcassonne most towns surrendered without a struggle. Albi, Castelnaudary, Castres, Fanjeaux, Limoux, Lombers and Montréal all fell quickly during the autumn. However some of the towns quickly taken later revolted.
The next struggle centred around Lastours and the adjacent castle of Cabaret. Attacked in December 1209 Pierre-Roger de Cabaret repulsed the attackers. Fighting largely halted over the winter but many new crusaders arrived. In March 1210 Bram was captured after a short siege. In June the well fortified town of Minerve was invested, it withstood a heavy bombardment but in late June the town's main well was destroyed and on July 22 the inhabitants surrendered, the Cathar residents were given a chance to convert and the 140 who refused were burned. In August the crusade proceeded to Termes and despite attacks from Pierre-Roger de Cabaret the siege was solid and in December the town fell. It was the last action of the year.
When action resumed in 1211 the actions of Arnaud-Amaury and Simon de Montfort had alienated several lords over the winter including Raymond of Toulouse, who had been excommunicated again. The crusaders returned in force to Lastours in March and Pierre-Roger de Cabarat soon agreed to surrender. In May the crusading force was directed against some revolters, the castle of Aimery de Montréal was retaken, he and his senior knights were hung and several hundred Cathars were burned. Cassès and Montferrand both fell easily in early June and the crusaders headed for Toulouse. The town was besieged but for once the attackers were short of supplies and men, and so Simon de Montfort withdrew before the end of the month. Emboldened Raymond of Toulouse led a force to attack de Monfort at Castelnaudary in September. De Montfort broke free from the siege but Castelnaudary fell and the forces of Raymond went on to liberate over thirty towns before grinding to a halt at Lastours in the autumn. The following year much of the province of Toulouse was re-captured.
In 1213 forces led by the king Peter II of Aragon, I of Catalonia came to the aid of Toulouse. The force besieged Muret, but in September a sortie from the castle led to the death of king Peter and his army fled. It was a serious blow for the resisters and in 1214 the situation became worse, Raymond was forced to flee to England and his lands were given by the Pope to the freshly victorious Philippe II, a ploy which succeeded in interesting the king in the conflict. In November the ever active Simon de Montfort entered Périgord and easily captured the castles of Domme and Montfort, he also occupied Castlenaud and destroyed the fortifications of Beynac. In 1215 Castelnaud was lost and swiftly recaptured by de Montfort and the crusaders entered Toulouse. Toulouse was gifted to de Monfort and in April 1216 he ceded his lands to Philippe.
However, Raymond together with his son returned to the region in April, 1216 and soon raised a substantial force from disaffected towns. Beaucaire was besieged in May and fell after a three month siege, the efforts of de Montfort to relieve the town were repulsed. De Montfort had then to put down an uprising in Toulouse before heading west to captured Bigorre but was repulsed at Lourdes in December 1216. In 1217 while de Montfort was occupied in the Foix region Raymond took Toulouse in September, de Montfort hurried back but his forces were inadequate to take the town before campaigning halted. De Montfort renewed the siege in the spring of 1218, in June while fighting in a sortie de Montfort was killed.
The crusade was left in temporary disarray. The command passed to the more cautious Philippe II and he was concerned with Toulouse rather than heresy. Innocent III had also died in July 1216. The conflict fell into something a lull until 1219, although the crusaders had taken Belcaire and besieged Marmande in late 1218 under Amaury de Montfort. Marmande fell on June 3, 1219 but attempts to retake Toulouse faltered and a number of de Montfort holds fell. In 1220 Castelnaudary was taken from de Montfort, and while Amaury de Montfort attacked the town from July 1220 the town withstood a eight month siege. In 1221 the success of Raymond and his son continued, Montréal and Fanjeaux were captured and many Catholics fled. In 1222 Raymond died and was succeeded by his son Raymond. In 1223 Philippe II died and was succeeded by Louis VIII. In 1224 Amaury de Montfort abandoned Carcassonne and fled, the son of Raymond-Roger de Trencaval returned from exile to reclaim the area. Amaury de Montfort offered his claim to the lands of Languedoc to Louis VIII and he accepted.
In November 1225 Raymond, like his father, was excommunicated. Louis VIII headed the new crusade into the area in June 1226, towns and castles surrendered without resistance. Avignon, nominally under the rule of the German emperor, did resist and it took a three month siege to finally subdue the town into surrendering in September. Louis VIII died in November and was succeeded by the child king Louis IX. But queen Blanche of Castile allowed the crusade to continue under Humbert de Beaujeu. Labécède fell in 1227 and Vareilles and Toulouse in 1228. However queen Blanche offered Raymond a treaty, recognizing him as ruler of Toulouse in return for fighting Cathars, returning all Church property, turning over his castles and destroying the defences of Toulouse. Raymond agreed and signed a treaty at Meaux in April 1229 he was then seized, whipped and briefly imprisoned.
Languedoc now was firmly under the control of the king of France. The Inquisition was established in Toulouse in November 1229 and the process of ridding the area of heresy and investing the remaining Cathar strongholds began. Under Pope Gregory IX the Inquistion was given almost unlimited power to suppress the heretics and from 1233 a ruthless campaign started, burning Cathars wherever they were found, even exhuming bodies for burning. Naturally many resisted, taking refuge in a few fortresses in Fenouillèdes and Montségur or inciting uprisings. In 1235 the Inquisition was forced out of Albi, Narbonne, and Toulouse. Raymond-Roger de Trencavel led a military effort in 1240, he was defeated at Carcassonne in October and then besieged at Montréal where he soon surrendered and was allow passage to exile in Aragon. In 1242 Raymond de Toulouse attempted a revolt to coincide with an English invasion, but the English were quickly repulsed and his support collapsed. Raymond was pardoned by the king.
The Cathar strongholds slowly fell, the largest at Peyrepertuse in 1240, Montségur withstood a nine month siege before being captured in March 1244. The final holdout, a small, isolated fort at Quéribus had been also overlooked until August 1255 when it quickly fell. The last Cathar burning by the Inquisition occurred in 1321.