The Decline and Fall of the Roman Empire
Romans, he believed, became unwilling to live the tougher, "manly" military lifestyle. In addition, Gibbon argued that Christianity created a belief that a better life existed after death. This fostered an indifference to the present among Roman citizens, and sapped their desire to sacrifice for the Empire. He also believed its pacifism tended to hamper the traditional Roman martial spirit. Finally, like other Enlightenment thinkers, Gibbon held in contempt the Middle Ages as a priest-ridden, superstitious, "dark age".  It was not until his own age of reason and rational thought, so it was believed, that human history could resume its progress.