The Decline and Fall of the Roman Empire by Edward Gibbon (complete audiobook, 19/63)

The History of the Decline and Fall of the Roman Empire is a six-volume work by the English historian Edward Gibbon. It traces Western civilization (as well as the Islamic and Mongolian conquests) from the height of the Roman Empire to the fall of Byzantium in the fifth century. Volume I was published in 1776 and went through six printings. Volumes II and III were published in 1781; volumes IV, V, and VI in 1788–1789.
The six volumes cover the history, from 98 to 1590, of the Roman Empire, the history of early Christianity and then of the Roman State Church, and the history of Europe, and discusses the decline of the Roman Empire among other things.

Gibbon offers an explanation for the fall of the Roman Empire, a task made difficult by a lack of comprehensive written sources, though he was not the only historian to attempt it.

According to Gibbon, the Roman Empire succumbed to barbarian invasions in large part due to the gradual loss of civic virtue among its citizens.

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.

Like other Enlightenment thinkers and British citizens of the age steeped in institutional anti-Catholicism, Gibbon held in contempt the Middle Ages as a priest-ridden, superstitious Dark Age. It was not until his own era, the "Age of Reason", with its emphasis on rational thought, it was believed, that human history could resume its progress.

"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, Chapter 38 "General Observations on the Fall of the Roman Empire in the West")