There's a theory that, believe it or not has some adherents, which proposes that the years 614-911 AD never happened.
Here's a summary of the theory from Damn Interesting (that's the name of the blog, the author is Allan Bellows).
DI comes to the conclusion that this theory is not worth the air it takes to explain it. I read the article with great interest, hoping that I could maybe find a way to wipe out my 30's. Alas, they remain.