Edward Gibbon, The Decline and Fall of the Roman Empire Vol. II:
“The Protestant and philosophic readers of the present age will incline to believe, that in the account of his own conversion, Constantine attested a wilful falsehood by a solemn and deliberate perjury. They may not hesitate to pronounce, that in the choice of a religion, his mind was determined only by a sense of interest; and that (according to the expression of a profane poet ) he used the altars of the church as a convenient footstool to the throne of the empire. A conclusion so harsh and so absolute is not, however, warranted by our knowledge of human nature, of Constantine, or of Christianity. In an age of religious fervor, the most artful statesmen are observed to feel some part of the enthusiasm which they inspire, and the most orthodox saints assume the dangerous privilege of defending the cause of truth by the arms of deceit and falsehood. Personal interest is often the standard of our belief, as well as of our practice; and the same motives of temporal advantage which might influence the public conduct and professions of Constantine, would insensibly dispose his mind to embrace a religion so propitious to his fame and fortunes. His vanity was gratified by the flattering assurance, that he had been chosen by Heaven to reign over the earth; success had justified his divine title to the throne, and that title was founded on the truth of the Christian revelation. As real virtue is sometimes excited by undeserved applause, the specious piety of Constantine, if at first it was only specious, might gradually, by the influence of praise, of habit, and of example, be matured into serious faith and fervent devotion. The bishops and teachers of the new sect, whose dress and manners had not qualified them for the residence of a court, were admitted to the Imperial table; they accompanied the monarch in his expeditions; and the ascendant which one of them, an Egyptian or a Spaniard, acquired over his mind, was imputed by the Pagans to the effect of magic. Lactantius, who has adorned the precepts of the gospel with the eloquence of Cicero, and Eusebius, who has consecrated the learning and philosophy of the Greeks to the service of religion, were both received into the friendship and familiarity of their sovereign; and those able masters of controversy could patiently watch the soft and yielding moments of persuasion, and dexterously apply the arguments which were the best adapted to his character and understanding. Whatever advantages might be derived from the acquisition of an Imperial proselyte, he was distinguished by the splendor of his purple, rather than by the superiority of wisdom, or virtue, from the many thousands of his subjects who had embraced the doctrines of Christianity. Nor can it be deemed incredible, that the mind of an unlettered soldier should have yielded to the weight of evidence, which, in a more enlightened age, has satisfied or subdued the reason of a Grotius, a Pascal, or a Locke.”