In 864 Tsar Boris I of the Bulgarian empire converted to Christianity after an extensive period of research into Christianity which included detailed questioning of the Pope. However, the new religion only took off after the intervention of the pupils of Saints Cyril and Methodius moved in after their expulsion from Moravia. The following decades saw a religious outpouring in Bulgaria with popular preachers, competing forms of monasticism, and the emergence of the dualist Bogomils. A society in flux was recorded by Kosmas Presbyter in his attempt to assess the state of the church and ward off the political disintegration which was looming.

Dr. Andrew Roach is Senior Lecturer at the University of Glasgow. He researches heresy, medieval religion, and the economics of religion. He is the author of The Devil's World: heresy and society, 1150-1320, and is working on a second edition.