When does does 'the Eastern Roman Empire' become 'Byzantium'?
Diocletian dividing the empire into east and west
Fall of Rome/Italy to the Goths
Rashidun Caliphate conqurs Egypt/Levant/Syria
Battle of Manzikert/loss of Anatolian plateau
Fourth Crusade
Other (later)
Other (in range but not mentioned)
never/'Byzantine' is a slur
vanilla extract
Fall of Rome to the Goths. Before that, you could honestly say the Eastern Roman Empire was the Eastern *Roman Empire*, the eastern half of a greater whole. Afterwards, the “Eastern Roman Empire” is all there is, it makes sense to identify it differently.
I would, however, date that to 455 rather than 476. The “Western Roman Empire” soldiered on after that point, but it wasn’t effectively part of the same polity as the East. Yes, even under Anthemius, who despite being appointed in the East still ruled on Ricimer’s sufferage, as proven by the fact that when they went head-to-head Anthemius lost.
As an additional point, the next Eastern emperor to be crowned after 455, Leo I in 457, was the first emperor to be crowned by Patriarch of Constantinople. Obviously, any cultural transition is going to be gradual, but I think that’s a pretty significant threshold.


