330 AD: Constantine founds the new capital of the Roman Empire on the existing site of the ancient Greek city Byzantium: Byzantium was renamed Constantinople and it would become the capital of the Byzantine Empire.
800: Charlemagne, king of the Franks, is crowned "Emperor of the Romans" by Pope Leo III in Rome. For the first time in 300 years, there is an emperor of the "East" and an emperor of the "West".