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.
History of Rome
Rome's population declined after its peak in the 2nd century. At the end of that century, during the reign of Marcus Aurelius, the Antonine Plague killed 2,000 people a day. Marcus Aurelius died in 180, his reign being the last of the "Five Good Emperors" and Pax Romana. His son Commodus, who had been co-emperor since AD 177, assumed full imperial power, which is most generally associated with the gradual decline of the Western Roman Empire. Rome's population was only a fraction of its peak when the Aurelian Wall was completed in the year 273 (in that year its population was only around 500,000).