In his fascinating paper, Professor Momigliano drew to our attention the degree to which the aristocracy of the late Roman Empire accepted within its religious ethos beliefs and practices which we would be inclined to label as ‘popular’. In doing so, he raised the recurrent problem of cultural diffusion. How far, in a given period, were intellectuals willing to accept as normative the piety of the simple faithful? Conversely, how far did the more critical attitudes of scholars influence popular devotion? These are permanent questions which we may ask of the history of the church, but perhaps the problem was never so acute as in the medieval church. Its intelligentsia (the humanists of the twelfth century, the philosophers of the thirteenth) had received a long and exacting formal education. The ordinary faithful, conversely, were illiterate, cut off, we might think, from the very sources of christian spirituality, for they could neither read the Scriptures nor follow the latin liturgy. Critics of the medieval church have been inclined to see two religions rather than one: a philosophical, indeed over-rational, religion of the intelligentsia, and a set of popular superstitions. A valuable piece of evidence in assessing the truth of this estimate is to be found in the first book of the treatise on The Relics of the Saints written in about 1120 by Guibert abbot of Nogent. Its significance lies, not only in the useful information which it contains about popular practice, but in the fact that it was an attempt to assess it, made by one of the more learned and attractive men of the time. Although Guibert made little direct impact on the history of the age, he was in close sympathy with many of the leaders of the twelfth-century Renaissance, and was a fine scholar in his own right.