This is a compelling introduction to the war against the heretics of Languedoc launched in 1209, combined with a description of the political. economic, religious and social conditions of south-western France in the twelfth and thirteenth centuries. Michael Costen shows why the Cathar heresy came to flourish and how the campaign against it developed into a programme of conquest by which an alliance of church and state finally destroyed the heresy and united the region with the newly expanding.