The Cité de Carcassonne is a medieval citadel located in the French city of Carcassonne, on a hill on the overlooking the River Aude. The town has about 2,500 years of history and has seen the Romans, Visigoths, Saracens and Crusaders.
In the early years of the 13th century, a sect of Christians called the Cathars had risen to prominence in the area. The Cathars believed in a dualistic theism, where the good god (God) created all that was spiritual and a bad god (Satan) created all that was material.
The Cathars managed to upset the Roman Catholic establishment to the point where they fled to and were laid siege upon in this fortress. For a year, local Catholics and Cathars fought against the siege of Arnaud-Amaury.
When asked how to distinguish Cathars from Catholics at the besieged town of Béziers, Arnaud replied "Caedite eos. Novit enim Dominus qui sunt eius" or "Slay them. God knows his own." This statement is often remembered as "Kill them all and let God sort them out."
