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. For most of Roman history, their religion is the Roman Pantheon. Now near the end of what is called the Roman Empire, when Constantine comes around in the early fourth century, Christianity gets legalized, and Theodosius, who is the last emperor to rule over both East and West, he makes Christianity the official religion. Since the Eastern Roman Empire's roots, the Byzantine Empire's roots, are considered to be with Constantine, it has a Christian nature from the beginning, and it only becomes more and more Christian over time.