Quality of Late Roman Legions

[Virilis]

All this leads to the basic question: Is it possible in general for an empire of this scale to survive for a longer period? I mean the ethnic, social, military, economical, logistical problems which comes along with an "empire" are such a burden that is it simply possible at all to keep it up in a coherent, static unit? I still believe that empires like these are surviving by the continuing dynamism brought by expansion & wars. Once the empire stops to expand, something very vital is lost at the same time... Don`t laugh.