It's fair to say that Rome was the capital of the Roman Empire from its early days as a kingdom all the way until the first several centuries of the Common Era. The roots of the Byzantine Empire are with Constantine changing the capital, the seat of power of the combined empire, and moving it from Rome to Byzantium, which will eventually be called Constantinople. Now let's think about language. So the language of the Roman Empire is Latin. In the early days of the Byzantine Empire, Latin is used in conjunction with Greek, but over time it becomes more Greek. In fact, Heraclius in the seventh century makes Greek the official language of the Byzantine Empire. Now religion.