On 15 August 1209, the city of Carcassone fell to the armies of Papal legate Arnaud Amaury.

The siege and capture of Carcassone was part of the Albigensian Crusade called by Pope Innocent III. The Albigensians or Cathars inhabited southern France. The Cathars did not accept the doctrine and teachings of the Catholic Church. They believed that there were two forces or gods – one that created the material world and was evil and the other who was pure spirit and was good. Since the good god was pure spirit, they denied the possibility of anything like the incarnation or the crucifixion – good spirit could not join evil matter. They also attacked what they called the corruption of the Catholic Church.

The Albingensians or Cathars did not take these names upon themselves. They were called Cathars [or Pure Ones] or Albigensians [for the French town of Albi where many of the Cathars lived] by others.

The spread of Albigensianism alarmed the Pope and he sent St. Dominic and his followers to call the Albigensians back to orthodox Catholicism. However, these missionary efforts did not meet with much success. After one of the Pope’s legates was murdered by a suspected Cathar, Pope Innocent III called for a Crusade against the Albigensians and promised their land to any who would wage war against them

Several towns were taken by the Crusaders. The Crusaders destroyed the town of Béziers, killing thousands of Cathar and Catholic alike.

While the town of Carcassone was strongly defended, it was full of refugees who had fled the Crusade. It fell on August 15. While the townspeople were not killed, they were forced to leave the town. One source says they were forced to leave the town naked, another says they were forced to leave “in their shifts and breeches”.

While the Crusade officially ended in 1229, the Catholic Church continued to act against the Cathars through the use of the Inquisition.