The Cathars spent much of 1209 fending off the crusaders . The Béziers army attempted a sortie but was quickly defeated , then pursued by the crusaders back through the gates and into the city . Arnaud-Amaury , the Cistercian abbot-commander , is supposed to have been asked how to tell Cathars from Catholics . His reply , recalled by Caesarius of Heisterbach , a fellow Cistercian , thirty years later was '' " Caedite eos . Novit enim Dominus qui sunt eius " '' — " Kill them all , the Lord will recognise His own " . The doors of the church of St Mary Magdalene were broken down and the refugees dragged out and slaughtered . Reportedly at least 7,000 innocent men , women and children were killed there by Catholic forces . Elsewhere in the town , many more thousands were mutilated and killed . Prisoners were blinded , dragged behind horses , and used for target practice . What remained of the city was razed by fire . Arnaud-Amaury wrote to Pope Innocent III , " Today your Holiness , twenty thousand heretics were put to the sword , regardless of rank , age , or sex . " " The permanent population of Béziers at that time was then probably no more than 5,000 , but local refugees seeking shelter within the city walls could conceivably have increased the number to 20,000 . " After the success of his siege of Carcassonne , which followed the Massacre at Béziers in 1209 , Simon de Montfort was designated as leader of the Crusader army . Prominent opponents of the Crusaders were Raymond Roger Trencavel , viscount of Carcassonne , and his feudal overlord Peter II , the king of Aragon , who held fiefdoms and had a number of vassals in the region . Peter died fighting against the crusade on 12 September 1213 at the Battle of Muret . Simon de Montfort was killed on 25 June 1218 after maintaining a siege of Toulouse for nine months
Massacre at Béziers
Massacre at Béziers
Catharism