It almost seems like this part of history never happened.

You have some occasional pop-ups like the birth of Islam, Charlemagne and the Viking raids, but other than that these 500+ years seem either utterly uneventful or completely forgotten.

What interesting shit went down in this historical blip?

Or another (perhaps even more interesting question) why was it "forgotten"?

(And yes, awaiting smartasses, I know that the Roman Empire didn't technically fall until 1453)