From 1145 to 1229 Cistercian monks, respected as twelfth-century Europe's holiest and brightest men, embarked on preaching missions against dissident Christians in southern France. The twelfth century witnessed a remarkable upsurge of religious dissent, and preaching offered the medieval Church its most potent instrument of propaganda. Monastic preachers aspired to quell the opposition with words alone, but their sermons also roused recruits for the holy war of crusading on domestic soil as well as abroad. Public preaching was not at all customary for monks: in fact, ecclesiastical tradition and legislation prohibited it. Preaching was reserved instead to the secular clergy – the bishops and priests who espoused the active life in engagement with the world. In contrast, the monastic rule imposed a vow of stability, permanence within the monastery, as part of its design for a life centred on contemplation. Moreover, the Cistercian order established itself on a principle of withdrawal from the world and creation of a model Christian community isolated from the wickedness of society. Despite all this, some Cistercians served as itinerant preachers traversing city and countryside in anti-heretical campaigns. Others plunged even more deeply into the confrontation, accepting posts as bishops and papal legates who aided and even directed the Albigensian Crusade, one of the cruellest medieval wars, and who contributed to establishing procedures of inquisition, codified and expanded in the 1230s. Scholarship on the Albigensian Crusade (1209–29) and the development of the Inquisition has not yet centred on the crucial role of Cistercian prelates and preachers.