Despite the name, the "Dark Ages" period of medieval history was not dark at all, far from it. While the old political structures associated with Rome had either collapsed or significantly changed, population grew in some areas, and Roman roads, infrastructure, and laws continued in some form, while new advancements were made, though some things did end up lost. Your challenge is to make the post-Roman period as "dark" as possible, and as conforming to the stereotypes of the medieval period people have OTL.