"Caedite eos. Novit enim Dominus qui sunt eius."
"Kill them. For the Lord knows those that are His own."
The supposed reply from Papal Legate Abbot Arnaud Amalric when told there were a large number of Catholics within Beziers.
According to Caesarius of Heisterbach:
"When they discovered, from the admissions of some of them, that there were Catholics mingled with the heretics they said to the abbot "Sir, what shall we do, for we cannot distinguish between the faithful and the heretics." The abbot, like the others, was afraid that many, in fear of death, would pretend to be Catholics, and after their departure, would return to their heresy, and is said to have replied "Caedite eos. Novit enim Dominus qui sunt eius - Kill them all for the Lord knoweth them that are His" (2 Tim. ii. 19) and so countless number in that town were slain."
Amalric's own account:
"While discussions were still going on with the barons about the release of those in the city who were deemed to be Catholics, the servants and other persons of low rank and unarmed attacked the city without waiting for orders from their leaders. To our amazement, crying "to arms, to arms!", within the space of two or three hours they crossed the ditches and the walls and Béziers was taken. Our men spared no one, irrespective of rank, sex or age, and put to the sword almost 20,000 people. After this great slaughter the whole city was despoiled and burnt."
Killing in the name of god is nothing new.