How could Revelation be about the fall of Rome when Rome didn’t fall until AD 476?

Question:

I intend to start teaching on Revelation soon.  I have a decent basic understanding of the book so far, but I have some unanswered questions about it.

I believe that John wrote the book around 95 AD during Domitian's reign.  From what I've read, John was released under Nerva's two-year reign.  Also, I don't think there was any persecution under Nerva, so this would have given Christians the time to anticipate the next flood of persecution under Trajan and Hadrian, as that is why the book is written (to provide comfort to Christian's battling persecution).

The problem I find is with the downfall of the Roman Empire.  It seems that "Babylon the Great" would fall, according to Revelation 18.  If this is talking about the Roman Empire, how do we reconcile this thought with history?  Rome did not fall until 476 AD.  And John stated what he was writing was about to take place.  Obviously, the church in that area had slipped deep into apostasy by the fifth century, and, of course, John is not writing to the apostate church.

So I guess my question is: What is the fall of Babylon if it's not the literal fall of the Roman Empire?

Thanks.