XXV. Victory of Christianity and Conversion of the Roman Empire.
Christianity was now acknowledged as the religion of both East and West. It had also grown strong enough to convert the barbarians who overran the West. It restrained and educated them under the lead of the papacy, so that its conquests now extended beyond the Roman empire.
Merivale (preface to Conversion of Roman Empire) attributes the conversion of the Roman empire to four causes: (1) the external evidence of apparent fulfillment of prophecy and the evidence of miracles, (2) internal evidence as satisfying the spiritual wants of the empire and offering a Redeemer, (3) the example of the pure lives and heroic deaths of the early Christians, and (4) the success which attended the Christian cause under Constantine. Gibbon (chapter xv of Decline and Fall) seeks to account for the phenomenal success of Christianity in the empire by (1) the zeal and enthusiasm of the early Christians, (2) the belief of Christianity in immortality with both future rewards and future retributions, (3) miracles, (4) the high ethical code and pure morals of professing Christians, and (5) strong ecclesiastical organization on imperial patterns. But neither of these lists of causes seems to account satisfactorily for the progress and success of the religion of Jesus.
1. Negative Causes:
This was due in the first place to negative causes--the moral and spiritual bankruptcy of the antique world, the internal rottenness and decay of heathen systems. All ancient national religions had failed and were abandoned alike by philosophers and the masses, and no universal religion for humanity was offered except by Christianity. Worship had degenerated into pure formalism which brought no comfort to the heart. An imperious demand for revelation was felt which no philosophy or natural religion could satisfy.
2. Positive Causes:
But it was to positive causes chiefly that the success of the new religion was due, among which were the zeal, enthusiasm, and moral earnestness of the Christian faith. Its sterling qualities were best shown in persecution and the heroic deaths of its adherents. Paganism, even with the alliance of the civil power and the prestige of its romantic past, could not withstand persecution. And when heathenism was thrown back on the voluntary system, it could not prosper as Christianity did with its ideals of self-sacrifice. The earnestness of early Christianity was raised to its highest power by its belief in a near second coming of the Lord and the end of the aeon. The means of propagation greatly helped the spread of Christianity, the principal means being the exemplary lives of its professors. It opposed moral and spiritual power to political. Besides, Christianity when once studied by the thinkers of the ancient world was found to be in accord with the highest principles of reason and Nature. But "the chief cause of its success was the congruity of its teaching with the spiritual nature of mankind" (Lecky). There was a deepseated earnestness in a large section of the ancient world to Whom Christianity offered the peace, comfort and strength desired. It was possessed also of an immense advantage over all competing religions of the Roman empire in being adapted to all classes and conditions and to all changes. There was nothing local or national about it; it gave the grandest expression to the contemporary ideal of brotherhood. Its respect for woman and its attraction for this sex gained it many converts who brought honor to it; in this respect it was far superior to its greatest rival, Mithraism. In an age of vast social change and much social distress it appealed to the suffering by its active self-denial for the happiness of others. As an ethical code it was equal and superior to the noblest contemporary systems. One incalculable advantage it could show above all religions and philosophies--the charm and power of an ideal perfect life, in which the highest manhood was held forth as an incentive to nobler living. The person of Jesus was an ideal and moral dynamic for both philosopher and the common man, far above any abstract virtue. "It was because it was true to the moral sentiments of the age, because it represented faithfully the supreme type of excellence to which men were then tending, because it corresponded with their religious wants, aims and emotions, because the whole spiritual being could then expand and expatiate under its influence that it planted its roots so deeply in the hearts of men" (Lecky, Hist of European Morals, chapter iii). Add to all this the favorable circumstances mentioned under "Preparation for Christianity," above (II), and we can understand how the Roman empire became the kingdom of Christ.

LITERATURE.
Ancient sources include Tacitus, Suetonius, Josephus, Plinys Letters, x.97-98 (in Hardys edition), Dio Cassius (in Xiphilin), the apologists, Church Fathers, Inscriptions, etc.
Modern sources are too numerous to mention in full, but those most helpful to the student are: Gibbon, Decline and Fall of the Roman Empire; Merivale, Hist of the Romans under the Empire; The Fall of the Roman Republic, 1856; Conversion of the Roman Empire, 1865; Milman, Hist of Christianity; Hist of Latin Christianity; Ramsay, The Church in the Roman Empire; The Expositor, IV, viii, pp. 8 ff, 110 ff, 282 ff; E. G. Hardy, Christianity and the Roman Government, 1894; D. Duff, The Early Church: a Hist of Christianity in the First Six Centuries, Edinburgh, 1891; J. J. Blunt, A Hist of the Christian Church during the First Three Centuries, 1861; Harnack, Mission and Expansion of Christianity, 1907; Mommsen, "Der Religionsfrevel nach rom. Recht," in Hist. Zeit, 1890, LXIV (important); Provinces of the Roman Empire; The Expositor, 1893, pp. 6 ff; G. Boissier, La religion romaine dAuguste aux Antonins; La fin du paganisme; Wissowa, Religion u. Kultus der Romer; Gerb. Uhlhorn, Conflict of Christianity with Heathenism, English translation by Smyth and Ropes, 1879; B. Aube, Histoire des persecutions de leglise jusqua la fin des Antonins, 1875; Schaff, Hist of the Christian Church (with useful bibliographies of both ancient and modern authorities); Orr, Neglected Factors in Early Church Hist; Keim, Rom u. Christentum; Deissmann, Light from the Ancient East, English translation, London, 1910; Wendland, Die hellenistischromische Kultur2, 1912; F. Overbeck, "Gesetze der rom. Kaiser gegen die Christen," in his Studien, 1875; C. F. Arnold, Die Neronische Christenverfolgung; Stud. zur Gesch. der Plinianischen Christenverfolgung; Westcott, "The Two Empires," in commentary to Epistles. of John, 250-82; Friedlander, Sittengeschichte Roms; Lightfoot, Apostolic Fathers; Lecky, Hist of European Morals, chapter iii. "The Conversion of Rome."
S. Angus