Catharism was the most successful heresy of the Middle Ages. Flourishing principally in the Languedoc and Italy, the Cathars taught that the world is evil and must be transcended through a simple life of prayer, work, fasting and non-violence. They believed themselves to be the heirs of the true heritage of Christianity going back to apostolic times, and completely rejected the Catholic Church and all its trappings, regarding it as the Church of Satan;...