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 of the Western Roman Empire was the process of decline in the Western Roman Empire in which it failed to enforce its rule. 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 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.
The story of its ruin is simple and obvious; and, instead of inquiring why the Roman empire was destroyed, we should rather be surprised that it had subsisted so long. The victorious legions, who, in distant wars, acquired the vices of strangers and mercenaries, first oppressed the freedom of the republic, and afterwards violated the majesty of the purple. The emperors, anxious for their personal safety and the public peace, were reduced to the base expedient of corrupting the discipline which rendered them alike formidable to their sovereign and to the enemy; the vigour of the military government was relaxed, and finally dissolved, by the partial institutions of Constantine; and the Roman world was overwhelmed by a deluge of Barbarians.
— Edward Gibbon. The Decline and Fall of the Roman Empire, "General Observations on the Fall of the Roman Empire in the West", Chapter 38
Alexander Demandt enumerated 210 different theories on why Rome fell, and new ideas have emerged since.
 Historians still try to analyze the reasons for loss of political control over a vast territory (and, as a subsidiary theme, the reasons for the survival of the
Eastern Roman Empire).
Comparison has also been made with China after the
end of the Han dynasty, which re-established unity under the
Sui dynasty while the Mediterranean world remained politically disunited.
Alternative descriptions and labels
At least from the time of
Henri Pirenne, scholars have described continuity of culture and of political legitimacy, long after 476. Pirenne postponed the demise of classical civilization to the 8th century. He challenged the notion that
Germanic barbarians had caused the
Western Roman Empire to end, and he refused to equate the end of the Western Roman Empire with the end of the office of
emperor in Italy. He pointed out the essential continuity of the economy of the Roman
Mediterranean even after the
barbarian invasions, and suggested that only the
Muslim conquests represented a decisive break with antiquity. The more recent formulation of a historical period characterized as "
Late Antiquity" emphasizes the transformations of ancient to medieval worlds within a cultural continuity. In recent decades archaeologically-based argument even extends the continuity in
material culture and in patterns of settlement as late as the eleventh century.
 Observing the political reality of lost control, but also the cultural and archaeological continuities, the process has been described as a complex cultural transformation, rather than a fall.