Catharism was the most successful heresy of the Middle Ages. The Cathars believed themselves to be heirs to the true Christian heritage, completely rejecting the Catholic Church and all of its trappings, and holding their services in fields, barns and people's homes. Alarmed at the movement's spread, the Catholic Church founded the Inquisition, and launched the Albigensian Crusade- the first to be directed against fellow Christians- which succeeded in exterminating virtually all trace of Catharism and was the first European act of genocide.