Pity poor Everard of Bucy, a northern French peasant who in 1114 interpreted the words of the Gospel, ‘Beati eritis’ (‘Blessed are you’), as ‘Blessed are the heretics’. Knowing no Latin yet confronted by a bishop determined to root out all challenges to orthodoxy, Everard was publicly excoriated, imprisoned and then burned by the mob. His death came at the beginning of what R I Moore terms a ‘War on Heresy’. Moore’s is a lucid narrative, rich in anecdote. The story he tells is essentially that of a confrontation between the centralising power of kings and bishops, ranged against the doomed traditions of the local, the feudal and the folkloric. Perhaps because other fears had prevailed, most notably the fear of paganism, the Church chose not to pry too carefully into the ‘popular’ beliefs of western Europe for most of the period from the fall of Rome to the eleventh century. Beginning in the 1020s, however, with the show trial and burning of a group of clergy in Orléans, the suspicion grew that heresy was on the increase. From the 1150s, fears were focused upon a particular departure from Catholic teaching: dualism, the belief that two principles govern creation. The principle of evil, personified in the Devil, made all that is fleshly or produced by sex, while the principle of good resided in the spirit or soul. It was the duty of believers in dualism, insofar as possible, to purify the soul by abstaining from sex and by refusing all food generated in coition.