History of Europe
In 395 Theodosius I, who had made Christianity the official religion of the Roman Empire, would be the last emperor to preside over a united Roman Empire. The empire was split into two halves: the Western Roman Empire centred in Ravenna, and the Eastern Roman Empire (later to be referred to as the Byzantine Empire) centred in Constantinople. The Roman Empire was repeatedly attacked by Hunnic, Germanic, Slavic and other “barbarian” tribes (see: Migration Period), and in 476 finally the Western part fell to the Heruli chieftain Odoacer.
Holy Roman Emperor
The Emperor was crowned in a special ceremony, traditionally performed by the Pope in Rome. Without that coronation, no king, despite exercising all powers, could call himself Emperor. In 1508, Pope Julius II allowed Maximilian I to use the title of Emperor without coronation in Rome, though the title was qualified as "Electus Romanorum Imperator" ("elected Emperor of the Romans"). Maximilian's successors adopted the same titulature, usually when they became the sole ruler of the Holy Roman Empire. Maximilian's first successor Charles V was the last to be crowned Emperor.