The century 1200-1300 witnessed multiple Crusades. These were not the Holy Land Crusades so familiar through film, novels and texts disseminated. These were Christian against Christian; or Christian against other Europeans still identifying with perhaps an Orthodox Christian missionary group, or their own ethnic groups. The Balkan Crusades encompass those Eastern Europe and Northern Europe Crusades. There were also Crusades in Sicily, etc.
Albigensian Crusades. The Crusade relevant to Carcassonne -- the Albigensian Crusade, named for the City of Albi where may Cathars lived. The Cathar Crusade in effect extended beyond the official dates. Initial forays and brutalities at the end of the 12th Century bloomed into a formal Crusade by Papal Bull in 1208, and continued with slaughters until the last found Cathar was killed or forcibly converted, mid-century. Bernard Gui was a well-known Dominican Inquisitor, see http://www.cathar.info/12050401_gui.htm. A review of his life and times can help in understanding the era.
Carcassonne: a huge walled city now repaired, reconstructed where needed to recreate a period and encourage tourists, with a modern city outside the walls.
Carcassonne is a UNESCO World Heritage site.
The Crusaders came here from Beziers, then on to Lavaur, Toulouse, Montsegur, and other strongholds. The Cathar genocide has been wiped from the tourist information except for this, a glossy fold-out tourist map, Carcassonne, Plan Touristique, with a flip side entitled "Historique". Summaries are given in many languages. It pays to know a little French to see how little we are told. Carcassonns, built where a Roman fortress once controlled the area. "Simon de Montfort led heavy battles against the heretics, who were protected by Raymond Trencavel, "Vicomte de Carcassonns." After the destruction, a Bastide was built, then burned. Cultural life today is very rich .....
The French is little better: keep asking, why and how is anyone heretic? You die if you interpret ambiguous texts differently from your neighbor? As to Carcassonne, it was also a Neolithic site, and after the Romans, Visigothic. Christian. Then Saracens occupied. I hadn't realized the Moors got this far. Then, in the 13th century (I am translating from the brochure) facing a Cathar heresy (? define terms. What dogma and compare it to actual words of Jesus. How heresy?), the Pope Innocent III declared declared a Crusade against the Albigensians (many Cathars were from Albi, not far away). The count Simon de Montfort took it in 1209 and took as prisoner Raymond Trencavel, viscount of Carcassonne, Given in 1226 to the Crown.... (how about what led to Carcassonne: Beziers, Trencavel moving to Montfort during siege under a flag of truce, then captured, and later killed while a prisoner, and all the Cathar lands confiscated, riches, belongings, how about expelling everyone there, never mind, dear, that's just old history.
I asked the historian at St. Nazaire how people saw that era now, and she said that they do not question. They are taught to believe what they are told, and to have faith.