slightly orthogonal to this, but the original motivation behind the 'dark ages' label was that for large parts of europe there are very few written records for the 5-7th centuries. e.g., we know practically nothing what happened in 5th century england because the only written source -- gildas -- is mostly concerned with pontificating about sinful behaviour in artful ways. even some actual people he mentions in passing get biblically coded nicknames so we have to make wild guesses who's he referring to. and that's our only source for pretty much a century.
