There ate a few vote regions which I think a full Roman revival must hold:
Italy, Greece, Spain, Egypt, North Africa, are the key atras. And the secondary areas are part of southeast France (Gallia narbonnesis)Anatolia and the Levant, and a good chunk of the balkans. The rhineland while wealthy is rather distant and opens up a new frontier.
The interesting thing is that a lot of these regions- Italy, Greece, Spain, Anatolia,- have long coastlines and rather mountainous terrain which makes holding them in their entirety rather more plausible, though far from easy. These regions also have plenty of common cultural and political history.
I add in Egypt because it is essential to any heegmon of the Mediterranean and if held by a hostile power means said power will be an existential threat, as both the Persians and the Arabs showed.