This new study argues that the religious attitude of the Roman army was a crucial factor in the Christianization of the Roman world. Specifically, by the end of the third century, there was a significant Christian presence within the army which was ready to act in the interests of the faith. Conditions at this time were thus ripe for the coming to power of a Christian emperor: when Constantine converted to Christianity he could rely upon the enthusiastic support of his Christian soldiers. Constantine strengthened his Christian base by initiating policies which accelerated the Christianization of the army. The continuation of these policies by Christian Roman emperors eventually allowed them to use the military as a vehicle for the suppression of paganism and ‘heretical’ Christian sects.