The Roman Empire

Even though Geoffrey of Monmouth and Sir Thomas Malory have the Roman Empire in full existence during the traditional Arthurian period, history tells us that, in the West, the Roman Empire ceased to exist in AD 476, though the Eastern or Byzantine Empire lasted for nearly 1.000 years longer.

Sir Thomas Malory states that Arthur defeated the Emperor Lucius Hiberius and was crowned Emperor of Rome by the Pope. Claris et Laris also supports the idea of the Roman Empire existing during Arthur's time, stating that the Emperor Thereus invaded Britain but was defeated.