'Kill them all, God will know his own'

One of the results of the Crusades to the Middle East was the impetus to crusade against dissenters within Christendom.

"The Albigensian Crusade was immensely popular in northern France because it gave pious warriors an opportunity to win a Crusade indulgence without traveling far from home or serving more than 40 days. During the first season the Crusaders captured Béziers in the heart of Cathar territory and—following the instructions of the papal legate who allegedly said, “Kill them all. God will know his own,” when asked how the Crusaders should distinguish the heretics from true Christians—massacred almost the entire population of the city. With the exception of Carcassonne, which held out for a few months, much of the territory of the Albigeois surrendered to the Crusaders. Command of the Crusade was then given to Simon, lord of Montfort and earl of Leicester, who had served during the Fourth Crusade. Abandoning the Crusade after it attacked the Christians at Zadar, Simon went to fight in the Holy Land."