In the final paragraph of the last volume of The Decline and Fall of the Roman Empire Edward Gibbon sketched the issues that had most concerned him. In the section of the list which covers the causes of the end of the Roman West one finds “the disorders of military despotism; the rise, establishment, and sects of Christianity; the foundation of Constantinople; the division of the monarchy; the invasion and settlements of the barbarians of Germany and Scythia.” All these issues had certainly attracted Gibbon's attention in previous volumes, although in an even more succinct précis he had placed particular emphasis on two factors: “I have described the triumph of Barbarism and Religion.”

In what follows I wish to examine the relationship between the “triumph of Religion” and the “Decline and Fall” of the west Roman Empire—taking “Decline and Fall” as the period from the fourth to the seventh centuries, and not in a strictly Gibbonian sense. Although one can certainly say that the Empire came to an end in the West at some point in the fifth or sixth century, my prime concern is not with the significance of the deposition of the last western emperor (nor even with the fall of the Empire), but rather with the difference between western Europe, and the western Mediterranean more broadly, in 300 and in 600. While this is not intended as a critique of Gibbon, his interpretation provides a useful scaffolding for examining the changes that took place between those two dates. The distinction between the late- and post-Roman western Mediterranean can be seen as illustrating a “Decline,” but, as will become clear, I doubt whether the qualitative judgement that the word implies is helpful when one considers the major changes that took place.

Even though Gibbon's concerns, most especially that of religion, will provide the main focus for the line of argument that I will put forward, it should be stated immediately that his summary can no longer be regarded as providing an adequate list of the causes of the fall of the west Roman Empire.