Malcolm Barber 
Crusaders and Heretics, Twelfth to Fourteenth Centuries [PDF ebook] 

These articles seek to understand the attitudes and reactions of medieval society to both external threat and internal dissension, whether real or imagined. The crusaders encompass the Templars and the Knights of St Lazarus, members of military orders committed to the cause of perpetual battle for the faith; more reluctant secular knights urged into the complicated conflicts of Latin Greece by the papacy; and peasant enthusiasts from northern France, ultimately turning their frustration on the clergy and the Jews. Heretics range from Cathars, real opponents of the Church, to the lepers, imaginary subverters of society, allegedly in league with the two other perceived enemies of Western Christendom, the Jews and the Muslims.