The lack of written records during the Dark Ages is a sign of a major civilizational regression.

Writing and learning retreated to a relatively small group - the clergy. The cities that had thrived under the empire - and the public works that supported them - disappeared.

There has been a historiographical tendency to downplay the significance of the fall of the Western Roman Empire and to euphemistically refer to it as a "transformation." But we're talking about a massive decline in literacy and economic activity, and there are all sorts of indicators (like average human height) that show that people were dramatically worse off.