A best-selling history of the Third Crusade, when the Catholic Church waged war against heretics in its own ranks

In 1208 Pope Innocent III called for a Crusade against a country of fellow-Christians. The new enemy was Raymond VI, Count of Toulouse, one of the greatest princes in Western Christendom, premier baron of all the territories in southern France where the langue d'oc was spoken. So began the Albigensian Crusade (named after the French town of Albi), which was to culminate in 1244 with the massacre of Cathars at the mountain fortress of Montségur.

This Crusade was the Catholic Church's response to the rapid growth of a rival Christian religion in the very heart of Christendom - the religion of the Cathars (or 'pure ones'). These heretics drew their strength from the consciousness of belonging to a faith that had never seen eye to eye with Catholicism and was more ancient than the Church itself. From the beginning this religious war was to show all the characteristics of a national resistance movement, so that in the end it was not just the survival of the Cathar faith that was at stake but also that of the Languedoc itself as an autonomous and independent region of France.