In Chapter XXVIII, Final Destruction of Paganism. Introduction of the Worship of Saints and Relics among the Christians of his Decline and Fall of the Roman Empire, Gibbon, at his most ornate, describes the end – more or less – of pagan worship under Theodosius towards the end of the 4th century. In fact, he devotes the entire chapter to this topic. Don't ignore the footnotes! You can link from the text below.
THE ruin of Paganism, in the age of Theodosius, is perhaps the only example of the total extirpation of any ancient and popular superstition, and may therefore deserve to be considered as a singular event in the history of the human mind. The Christians, more especially the clergy, had impatiently supported the prudent delays of Constantine and the equal toleration of the elder Valentinian; nor could they deem their conquest perfect or secure as long as their adversaries were permitted to exist. The influence which Ambrose and his brethren had acquired over the youth of Gratian and the piety of Theodosius was employed to infuse the maxims of persecution into the breasts of the Imperial proselytes.
Two specious principles of religious jurisprudence were established, from whence they deduced a direct and rigorous conclusion against the subjects of the empire who still adhered to the ceremonies of their ancestors: that the magistrate is, in some measure, guilty of the crimes which he neglects to prohibit or to punish; and that the idolatrous worship of fabulous deities and real daemons is the most abominable crime against the supreme majesty of the Creator. The laws of Moses and the examples of Jewish history (1) were hastily, perhaps erroneously, applied by theclergy to the mild and universal reign of Christianity.(2) The zeal of the emperors was excited to vindicate their own honour and that of the Deity; and the temples of the Roman world were subverted about sixty years after the conversion of Constantine.
After a concise history of polytheism in ancient Rome, which around 384 was still practiced by the Senate in Rome, Gibbon describes at length its oppression and destruction.
And then he has his revenge:
In the period of twelve hundred years, which elapsed between the reign of Constantine and the reformation of Luther, the worship of saints and relics corrupted the pure and perfect simplicity of the Christian model; and some symptoms of degeneracy may be observed even in the first generations which adopted and cherished this pernicious innovation.
I. The satisfactory experience that; the relics of saints were more valuable than gold or precious stones (75) stimulated the clergy to multiply the treasures of the church. Without much regard for truth or probability, they invented names for skeletons, and actions for names. The fame of the apostles, and of the holy men who had imitated their virtues, was darkened by religious fiction. To the invincible band of genuine and primitive martyrs they added myriads of imaginary heroes, who had never existed, except in the fancy of crafty or credulous legendaries; and there is reason to suspect that Tours might not be the only diocese in which the bones of a malefactor were adored instead of those of a saint.(76) A superstitious practice, which tended to increase the temptations of fraud and credulity, insensibly extinguished the light of history and of reason in the Christian world …II. … If we enlarge our view to all the diocese, and all the saints, of the Christian world, it will not be easy to calculate the fables, and the errors, which issued from this inexhaustible source. But we may surely be allowed to observe that a miracle, in that age of superstition and credulity, lost its name and its merit, since it could scarcely be considered as a deviation from the ordinary and established laws of nature.
III. … The imagination, which had been raised by a painful effort to the contemplation and worship of the Universal Cause eagerly embraced such inferior objects of adoration as were more proportioned to its gross conceptions imperfect faculties. The sublime simple theology of primitive Christians was gradually corrupted: and the MONARCHY of heaven, already clouded by metaphysical subtleties, was degraded by the introduction of a popular mythology which tended to restore the reign of polytheism.(85)
IV. … The walls were hung round with symbols of the favours which they had received; eyes, and hands, and feet, of gold and silver: and edifying pictures, which could not long escape the abuse of indiscreet or idolatrous devotion, represented the image, the attributes, and the miracles of the tutelar saint. The same uniform original spirit of superstition might suggest, in the most distant ages and countries, the same methods of deceiving the credulity, and of affecting the senses of mankind:(89) but it must ingenuously be confessed that the ministers of the catholic church imitated the profane model which they were impatient to destroy. The most respectable bishops had persuaded themselves that the ignorant rustics would more cheerfully renounce the superstitions of Paganism, if they found some resemblance, some compensation, in the bosom of Christianity.
The religion of Constantine achieved, in less than a century, the final conquest of the Roman empire: but the victors themselves were insensibly subdued by the arts of their vanquished rivals.(90) (emphasis mine)
