In the century and a half after Constantine, three major changes took place in the Roman Empire. First, imperial control of the western half of the Empire weakened. Second, due to the move from Rome to Constantinople, Greek gradually replaced Latin as the Empire's dominant language. Finally, all but one of Constantine's successors were Christians, and Christianity went from being a persecuted sect to the Empire's official religion.
| Roman Empire | Byzantine Empire | |
| Capital | Rome | Constantinople |
| Religion | Paganism | Christianity |
| Language | Latin | Greek |
Historians call the Constantinople-centered, Greek-speaking Christian Empire the "Byzantine Empire" (after Constantinople's original name, Byzantium) to distinguish it from the Rome-centered, Latin-speaking pagan "Roman Empire." The "Byzantines" themselves, however, recognized no such distinction, and continued to refer to themselves as Romans for another thousand years.
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