The empire was divided into two halves by Diocletian in 284. It would be reigned as a whole again by several emperors after, but that is marked as the first occasion on which the split happened. It was in other words a continuation of part of the empire. One could also say it was the successor, as it now claimed the title of Empire and Emperor for itself, a title that would remain highly coveted by many others throughout the middle ages, mainly the German kings and emperors.