Once Christian monasticism had successfully transplanted itself from the deserts of North Africa to the more tem-perate climate of Western Europe in the early medieval period, it needed to reposition itself in the great cosmo-logical warfare of Christianity, and miracle tales became a key instrument for doing this. We might think of these tales involving the Devil, demons, demoniacs, and visions of or visits to Hell as indicating that medieval Christians were gullible and credulous, but these tales were as important to European monasticism as they had been to North African desert eremitism. Perhaps even more so, since monasteries were no longer situated in remote desert locations where the conditions of spiritual combat were evident, but were now often centrally positioned in or near European towns and on busy waterways and travel routes. Complete isolation was no longer possible for the medieval monk in terms of urban geography but could be reestablished on the spiritual plane so that the monk could continue to be seen as a warrior on the frontline of a battle with demonic forces, a vital advance-guard in the protection of Christian Europe. Monastic miracle tales told in the cloisters reinforced to the monks the importance of the role they were playing in society.

We can get a sense of how the demonic formed a key battle-line in medieval monasticism from one of the most powerful monks of twelfth-century Europe, Peter the Venerable. Peter was abbot of Cluny, a highly influential Benedictine monastery in France. At this time, abbots and abbesses could be figures of great political power in Europe, consulted by local landholders (counts, dukes, earls), kings and queens, and even the pope himself. Peter's actions as abbot and his writings convey a clear sense of the boundaries that Western monasticism needed to reify and fortify. Peter was the author of one of the most potent anti-Semitic tracts of twelfth-century monasticism, Against the Inveterate Obduracy of the Jews. He was also one of the first Christian leaders to engage with the increasingly powerful and geographically diverse Islamic faith, commissioning the first Latin translation of the Quran and then opposing its doctrines in his treatise Against the Saracens. Focusing then on doctrinal issues within the Christian faith itself, Peter wrote a tract against the Petrobrusian heresy associated with the figure of Peter of Bruys, who was put to death in 1131.