These accounts of medieval Manichees have almost always been taken at face value by historians. Mani's disciples proved remarkably resilient — they spread his teachings to China — so why not accept that they had survived Roman imperial persecution, to resurface in the post-Roman West? In the 1970s, however, R.I. Moore and others started to call this presumption to account. The War on Heresy is itself part two of what has been a long campaign. To begin with, Moore showed that the 11th-century accusations of "Manicheism" were not evidence of subterranean dissident continuity. They could far more plausibly be explained as the pinning of an inherited cultural category on to groups who were protesting against the new exercise of power by clerical and secular elites. These were not Manichees; they were local community activists, taking a stand against the claims of centralising governmental regimes. For this was the era of European "take off" (caught here in a telling detail: for the first time since Attila, the wealthy wore their fur inside, not outside, their garments).

Now Moore has taken the next and conclusive step. In his earlier work, he assumed, as everyone else did, that Manichee dualism really did appear in the 12th-century West, thanks to missionaries from Bulgaria. This story he has now abandoned. Once the texts condemning dualist heretics are lined up in chronological order of production, from the 1140s down to the 1250s, then their value as evidence for the crime of dualist heresy falls down like dominoes. The tentative use of the heresy accusation in one generation becomes the next generation's certainty. The Manichees whom churchmen sought out were transparently a product of the dualism in their own minds.

Why has it taken us so long to see this? One answer is that our very structures of critical inquiry are implicated in the production of the heresy accusation. The medieval university, devised to train minds for the service of the Church and the state, was the laboratory for the development of inquisitorial procedures. The War on Heresy is a triumph, even as it stares this problem in the face. Let us hope that we can say the same for the Chilcot report.