alternatehistory.com

For your challenge, should you choose to accept it, make it so that the Roman Empire collapses, but the Romans are able to survive in Britain as an Imperial state, similar to the Byzantines in the East. It's capital and core centered in Britain. For additional points, even have them reconquer some of the former empire e.g. Northern France.

POD is... let's go with anything as long as its after 350 AD.
Good luck!
Top