In 1163, a Church council gathered at Tours under the presidency of the spiritual leader of western Christendom, Pope Alexander III, and the protection of the formidably powerful king of England and ruler of Normandy, Anjou and Aquitaine, Henry II. Out of this imposing meeting came an alarming declaration: "In the district of Toulouse a damnable heresy has recently arisen, which, like a cancer gradually diffusing itself over the neighbouring places, has already infected vast numbers..."
This, R.I. Moore tells us, was the moment when the medieval "war on heresy" was publicly declared. There could be no doubt, once the council had spoken, that the Christian West was under attack by a shadowy underground organisation that threatened the safety and the well-being of its people. It was the duty of spiritual and political leaders to seek out this hidden threat. Failure to find it would demonstrate only that the powers-that-be had not searched with sufficient determination. Fortunately, the council knew exactly where the hunt should begin: the region of Toulouse, which - it just so happened - had been slow to respond to previous assertions of papal control, and quick to resist Henry II's attempt to conquer it four years earlier.
In this convenient confluence of paranoia and political advantage, the 12th century's "war on heresy" is alive with resonance for readers living through the 21st century's War on Terror - and, in Moore's skilful hands, these echoes across the centuries are not glib or (his title aside) even explicit, but troubling and thought-provoking.
The absorbing tale that forms Moore's subject was, until recently, settled in its outline. A heretical movement, given various names by contemporaries but known to history as "Catharism", spread west from Bulgaria during the 12th century, finding fertile soil for its beliefs in northern Italy, Rhineland Germany and, especially, southern France. The Cathars were dualists - that is, they believed that, while God created the incorruptible world of the spirit, the material world of the flesh was the work of the Devil. They therefore embraced a life of asceticism, abstaining from sex and from consuming meat and milk, and rejected the authority and the sacraments of what they saw as a fatally compromised Church. By the second half of the 12th century they had developed a spiritual organisation of their own, only to find themselves confronted with waves of persecution, most appallingly in the massacres and mutilations of the early 13th-century Albigensian Crusade.
But Moore strips this story to its foundations. It is, he says, a tale told backwards, both chronologically - in historians' willingness to extrapolate earlier developments from later sources - and analytically, given that the vast majority of the evidence for "Cathar" belief and practice comes from the hostile accounts of inquisitors and chroniclers who reviled them.
Instead, he begins at the beginning, and insists that texts can be read only in the most specific and sensitively reconstructed context, combining an anthropologist's eye for the workings of communities with a medievalist's grasp of the technicalities of testing sources to produce a layered, cumulative and compelling evocation of the lived experience of faith and dissent, out of which progressively more startling conclusions emerge.
Without fail, accusations of heresy were intimately linked with political conflict on a local or national scale. The line between orthodoxy and heresy among proponents of apostolic poverty in the reform movement of the 11th and 12th centuries was so fine as to be, at times, indistinguishable - and the grey area thus created offered ample scope for the politicisation of heresy to gather pace. Meanwhile, the identification of a coherent dualist heresy, complete with its own church structure, owed far more to the expectations and anx-ieties of the scholastic theologians who framed the inquisitions into its existence than it did to anything they actually encountered.
This is an account, then, in which "Catharism" ceases to exist as an independent phenomenon, becoming instead a phantom in the minds of those who went looking for it, and a political weapon to be used by the powerful against the weak. Moore's searching conclusions won't find universal acceptance; but his remarkable book stands as a brilliant demonstration of the infinitely challenging truth that the questions we ask - whether as inquisitors of our own time or as historians of another - profoundly shape the answers we find.
The War on Heresy: Faith and Power in Medieval Europe
By R.I. Moore
Profile, 416pp, £25.00
Published 15 March 2012