Presenting more coherent doctrinal opposition to the Catholic church than any other movement of the 12th and early 13th century, the dualist Cathars were spread throughout Christendom but particularly concentrated in southern France and northern Italy. Barber (history, U. of Reading) traces the origins and spread of dualist ideas, reactions by church and lay authorities, the development of radical religious beliefs, and the means of suppressing it. From the events, he culls issues about the nature of evil, the ethics of warfare, and the use made of history by later generations.