When did the Roman Empire fall (your thoughts)?

[M. Demetrius]

So, one could argue that being pro-Roman was the traditional Christian position.

Maybe, but simply not being "against" doesn't require being "for" in a political sense, Mt. 12:30 notwithstanding. It would be hard to make the case of their being pro-Roman to Christians living in Rome under Nero or Domitian, I'd reckon.

As a slight aside, there is a book titled How the Irish Saved Civilization which gives an account of Patricius' youth and education, and his subsequent efforts to preserve literature around the time we generally consider the "Fall" to have taken place. It gives some good insight into how some of the people living at that time viewed things, even though it doesn't claim to be a scholarly work of history, it's a good read, and most everything said there pertains to the times we're discussing here.