The common date given for the fall of Roman Empire is 476 CE. This is the date when Flavius Odoacer, a barbarian, overthrew the Western Emperor Romulus Augustulus and seized control of the Western Roman Empire. But it is a bit more complicated than that because the Eastern Roman Empire continued to exist until 1453 CE.

The assassination of Emperor Severus Alexander in 235 CE brought the empire close to collapse as a civil war raged for almost fifty years – in which at least 26 individuals laid claim to the title of Emperor of the Roman Empire. This is known as the Crisis of the Third Century. It was put to an end by Emperor Diocletian in 284 CE. Diocletian restructured the empire to have four co-emperors – known as a Tetrarchy (from the Greek tetra- (four) + -arkhia (rule)). This was not seen by the Romans as a division of the empire, but a practical approach to its effective administration. However, this structure was unstable.

When Constantine the Great became emperor of of the North-Western territories — including Britain, Gaul, and Spain in 306 CE, his rule was challenged by Emperor Maxentius of Rome. Constantine defeated Maxentius in 312 CE and took over his share of the Empire. The previous year, Emperor Licinius had defeated Emperor Galerius and ruled as the emperor over the eastern half of the empire. In 324 CE, Constantine defeated Licinius and became sole emperor of the Roman Empire.

In 330 CE, Emperor Constantine moved the capital of the Roman Empire eastward, from Rome to Byzantium. After his death, the city was renamed Constantinople and his three sons – Constantine II, Constantius II and Constans – ruled as co-emperors – returning, somewhat, to Diocletian’s recognition that the empire was too large to be effectively ruled from a single administrative location. The Roman Empire had multiple Emperors, the chief of which was located in the eastern city of Constantinople.

When Odoacer deposed the official Roman authority in Rome, he sent back the Roman standards signaling that the Roman Empire no longer had authority or control in the West.

The eastern half of the Empire became known as the Byzantine Empire and remained the continuation of the Roman Empire until the defeat of Constantinople by the Ottomans in 1453 CE.