the Bogomil heresy was the last of the dualist heresies to plague the orthodox church, which it did down to the end of the middle ages. It fed on popular piety, customs and superstitions. It had almost nothing in common with the ‘philosophical’ heresies of the eleventh and twelfth centuries. These belong to the intellectual history of the Byzantine Empire and were part of the squabbling, often of a political character, that went on in the struggle for preferment within the precincts of the patriarchal church. The only thing that unites a John Italos and a Basil the Bogomil was that they would both be arraigned by the Emperor Alexius I Comnenus on charges of heresy. There was on both occasions a high political content in the charges of heresy. It was a useful way of cowing political opponents and asserting authority in the streets and squares of Constantinople. Heresy could also be a figment of official paranoia. Any hint of nonconformity might be taken as political subversion. But one should resist the temptation to explain heresy away in this fashion. The Byzantine authorities were dealing with a real phenomenon, even if they misunderstood it and had every reason to misrepresent it and exaggerate it.

From its earliest days the Christian church had singled out dualism as a major threat. Among other things it offered an attractive solution to Christianity's Achilles' heel – the problem of evil.