Relevant dates include 117 CE, when the Empire was at its greatest territorial extent, and the accession of Diocletian in 284. Irreversible major territorial loss, however, began in 376 with a large-scale irruption of Goths and others. In 395, after winning two destructive civil wars, Theodosius I died, leaving a collapsing field army and the Empire, still plagued by Goths, divided between his two incapable sons. By 476 when Odoacer deposed the Emperor Romulus, the Western Roman Emperor wielded negligible military, political, or financial power and had no effective control over the scattered Western domains that could still be described as Roman. Invading barbarians had established their own power in most of the area of the Western Empire. While its legitimacy lasted for centuries longer and its cultural influence remains today, the Western Empire never had the strength to rise again.
The Fall is not the only unifying concept for these events; the period described as Late Antiquity emphasizes the cultural continuities throughout and beyond the political collapse.
Since 1776, when Edward Gibbon published the first volume of his The History of the Decline and Fall of the Roman Empire, Decline and Fall has been the theme around which much of the history of the Roman Empire has been structured. "From the eighteenth century onward," historian Glen Bowersock wrote, "we have been obsessed with the fall: it has been valued as an archetype for every perceived decline, and, hence, as a symbol for our own fears." The Fall is not the only unifying concept for these events; the period described as Late Antiquity emphasizes the cultural continuities throughout and beyond the political collapse.
The Fall of the Western Roman Empire was the process of decline in the Western Roman Empire in which it failed to enforce its rule. The loss of centralized political control over the West, and the lessened power of the East, are universally agreed, but the theme of decline has been taken to cover a much wider time span than the hundred years from 376. For Cassius Dio, the accession of the emperor Commodus in 180 CE marked the descent "from a kingdom of gold to one of rust and iron". Gibbon started his story in 98 and Theodor Mommsen regarded the whole of the imperial period as unworthy of inclusion in his Nobel Prize-winning History of Rome. Arnold J. Toynbee and James Burke argue that the entire Imperial era was one of steady decay of institutions founded in republican times. As one convenient marker for the end, 476 has been used since Gibbon, but other markers include the Crisis of the Third Century, the Crossing of the Rhine in 406 (or 405), the sack of Rome in 410, the death of Julius Nepos in 480, all the way to the Fall of New Rome in 1453.
Gibbon gave a classic formulation of reasons why the Fall happened. He began an ongoing controversy about the role of Christianity, but he gave great weight to other causes of internal decline and to attacks from outside the Empire.