What is also clear is that Celsus is more than just disdainful. He is worried. Pervading his writing is a clear anxiety that this religion—a religion that he considers stupid, pernicious and vulgar—might spread even further and, in so doing, damage Rome. Over 1,500 years later, the eighteenth-century English historian Edward Gibbon would draw similar conclusions, laying part of the blame for the fall of the Roman Empire firmly at the door of the Christians. The Christians’ belief in their forthcoming heavenly realm made them dangerously indifferent to the needs of their earthly one. Christians shirked military service, the clergy actively preached pusillanimity, and vast amounts of public money were spent not on protecting armies but squandered instead on the “useless multitudes” of the Church’s monks and nuns. They showed, Gibbon felt, an “indolent, or even criminal, disregard for the public welfare.  

The Catholic Church and its “useless multitudes” were, in return, magnificently unimpressed by Gibbon’s arguments, and they promptly placed his Decline and Fall of the Roman Empire on the Index Librorum Prohibitorum, its list of banned books.

Even in liberal England, the atmosphere became fiercely hostile to the historian. Gibbon later said that he had been shocked by the response to his work. “Had I believed,” he wrote, “that the majority of English readers were so fondly attached even to the name and shadow of Christianity . . . I might, perhaps, have softened the two invidious chapters, which would create many enemies, and conciliate few friends.”

Celsus did not soften his attack either. This first assault on Christianity was vicious, powerful and, like Gibbon, immensely readable. Yet unlike Gibbon, today almost no one has heard of Celsus and fewer still have read his work. Because Celsus’s fears came true. Christianity continued to spread, and not just among the lower classes. Within 150 years of Celsus’s attack, even the emperor of Rome professed himself a follower of the religion.

(From The Darkening Age: The Christian Destruction of the Classical World by Catherine Nixey)