CHRISTIANITY was the Franks’ religion. When Rollo was given Rouen and its hinterland by Charles the Simple he was obliged to convert and conform. Rouen was worth a Mass, but Rollo's authority was now subject to a religion he did not control but by which he would be judged. This was a new problem for a Scandinavian lord. The kings of Denmark and Norway had still to convert their people to Christianity in 911, and in the meantime there was no institutionalized religion in those countries, and thus no central control of it. But while the Danes and Norwegians did not have control over religion, it is also the case that they did not live with a religion that operated within their territory but which was under the control of someone else. The potential for disunity that such a rival authority brought with it must have become clear to the new duke very quickly. Fortunately for Rollo, the disruption brought by the Viking raiding of the ninth century ensured that it would be some time before the Church was in a position to be used against him or his successors. Indeed, it was only in 990 that the scribe of a ducal act could remark on the simultaneous existence of bishops for all seven of the dioceses of the province of Rouen. And by then the Franks were no longer in control. Instead, Richard I and his brother, Archbishop Robert of Rouen, stood at the helm of the Norman Church, even if their authority would not be undisputed.

Chief among their, and their successors’, rivals were the popes. The advent of the so-called reform papacy in the middle of the eleventh century, and with it a greater desire to unify and oversee religious practices, led to a greater interference by the popes in Norman affairs. This was not always welcome. The dukes might on occasion seek the pope's help when they were preparing the diplomatic ground work for, by way of example, the deposition of Archbishop Malger in 1054 or 1055 or the transfer of Bishop John of Avranches to the archbishopric of Rouen c. 1066, but they opposed appeals to papal authority by their subjects when those appeals infringed their own authority and freedom of action.