The Byzantine Empire

Each part of the empire would be led by a senior emperor called the augustus. The system was known as the tetrarchy and lasted for about 20 years. After diocletian's death in year three 12, the two parts were unified once again under the rule of Emperor constantine the first. And this is the first possible starting point for the byzantine empire. Constantine founded the city of constantinople and legalized christianity in his empire. But he was, in every sense of the word, a true roman emperor.