A Roman Empire that doesn't fall. It absorbs enough of the invaders to settle Gaul and further east into Germania. Rome becomes China-like, and assimilates the constant stream of invaders when possible, and destroying those who don't stand with them. You get a border that wanders back and forth, but slowly expands farther and farther east as control solidifies to the west. Britannia may be abandoned to move forces back onto the mainland. With a Rome that is successful against the Germans, the invasions of Britain are limited and pushed back.
Perhaps, then, you'd get Europe consisting of the entire Roman world and Roman allies, and everything beyond the borders being a continent separate. Basically, Europe includes North Africa, the Levant, and Anatolia and other possessions, but doesn't include Scandinavia and most of modern day Russia.