“Catharists” (from the Greek word ϰαθαροί, pure) has been, since 1163, the most common and apt name for the largest of medieval sects; its own names (Christiani, boni homines), and the names coined by its opponents (Manichaeans, Patarines, Albigenses, also neo-Manichaeans) are scientifically unsuitable.

1. History. The first Catharists appeared in Cologne in 1143, having come from the Balkans together with merchants and crusaders; they spread quickly to England and Spain, and particularly to southern France and northern Italy. They combine…