Chateau Comtal is a fine example of the Cathar Castles that dot southern France. In their day - from about 1150 until the last of the Cathar heretics was burned at the stake in 1321 - the Cathars were a huge pain for the Catholic Church. They acknowledged neither papal authority nor his infallibility. Their leaders who wore simple clothing and were often without shoes scorned the wealth of the papacy. Their lives were all about service in stark contrast to the lives of those in church authority who sold indulgences to sinners. Cathars did not believe in Heaven or Hell, but rather in the perfection of the spirit over multiple lives. They banded together under various wealthy land barons who built castles in which both land owner and poor peasant could find protection.
The church sent armies of knights to destroy them. They were often tortured. Sometimes the Cathars were able to stand off the sieges. Sometimes walls fell and whole villages were slaughtered. One famous quote "Kill them all. God will sort them out," rather sets the tone for how the Catholic Knights felt about their Cathar brothers. You can read all about the Cathars at http://www.catharcastles.info.
One great story tells a version of how Carcassonne got its name. After a particularly long and difficult siege, Madame Carcas threw the last of the pigs over the wall. Taking this as a sign the castle was still well provisioned, the invaders folded their tents and went away. Unfortunately, although she stands in stone just outside the walls, there is no credibility to her story.
He made thousands of drawings as he reengineered the castle.You can read about him at http://en.m.wikipedia.org/wiki/Eugène_Viollet-le-Dic.
All in all this represents an interesting part of Christain history most of us would rather not know about. But it is a fairy tale setting.