Conversion of Constantine to Christianity Summary

  • Last updated on November 11, 2022

The conversion of Constantine marked the emergence of Christianity as the dominant religion of the slowly disintegrating Roman Empire, a development that led to the creation of a common European culture.

Summary of Event

By the end of the third century c.e., the Roman Empire was politically and religiously divided and in decline. Diocletian, one of the claimants to the title of Roman emperor, in an attempt to create religious and cultural unity, issued a series of decrees beginning in 303 c.e. against Christianity. The decrees included instructions to burn churches, destroy copies of the Scripture, and eventually to murder Christians themselves. After the abdication of Diocletian in 305, at least eight rivals emerged to claim the imperial title. By 312, only four remained: Maxentius and Maximinus Daia were aligned against Constantine and Licinius and continued the policy of encouraging religious unity by persecuting Christians. After Constantine defeated Maxentius at the Battle of Milvian Bridge (312) and Licinius conquered Maximinus Daia, the two victors divided the Roman Empire between them. The division lasted for ten years until Constantine defeated Licinius in 324 and became sole ruler. Constantine the Great Maxentius Licinius, Valerius Licinianus





At noon on the day before the battle against Maxentius at Milvian Bridge, Constantine, according to Eusebius of Caesarea’s Vita Constantini (339 c.e.; Life of Constantine, 1845), saw a sign appearing in the sky as a fiery cross with the legend: “Conquer by this.” The same night, the Christian God allegedly appeared to him in a dream and instructed him to place the Christian emblem on the imperial standards if he wished to be victorious. Eusebius claims that he heard the story from the lips of Constantine, but he wrote after the emperor’s death and he does not tell the same tale in his Historia ecclesiastica (c. 300, 324 c.e.; Ecclesiastical History, 1576-1577, better known as Eusebius’s Church History). At the head of his legions, Constantine placed the labarum displaying the first two letters of the word “Christ” in Greek, combined to form a cross. Subsequent victory against Maxentius convinced Constantine that the Christian God was more powerful than the classical deities worshiped by his rivals. Clearly Constantine was taking a risk because only about one-tenth of the Roman Empire was Christian at the time.

Constantine (seated).

(Library of Congress)

Whether the emperor’s conversion was contrived or genuine is still a matter of debate, but there can be no doubt that his rule was beneficial for Christianity. In 313 c.e., Licinius agreed on the terms of the Edict of Milan, which granted toleration to Christianity, reimbursed Christians for losses suffered in recent persecutions, and exempted the clergy from certain compulsory civil obligations. Although the edict continued to provide support for the continuance of traditional forms of Roman religion and simply affirmed toleration of Christianity, subsequent legislation certainly provided Christianity with a favored status. In 315, Constantine enacted legislation that prohibited retribution against Jewish converts to Christianity, and in 318, the emperor ordained, in a precedent-making decree, that a civil suit might, with the consent of both litigants, be removed to the jurisdiction of a bishop, whose verdict would be final. By 321, the Church could inherit property, and bishops could manumit slaves. Sunday was declared a holiday for imperial employees. By convening councils at Arles and Nicaea, Constantine set up ecclesiastical machinery for the adjudication of problems caused by dissenting groups such as Donatists and Arians. At the first ecumenical council, the emperor himself put his prestige behind the homoousian formula (the idea that Jesus Christ, the Son, had the same essence or substance as the Father, or God), which has remained Christian dogma ever since. Associating his Christian piety with the welfare of the state, Constantine built basilicas, composed prayers, and paid for translations of the Christian Scriptures. Finally, he was baptized on his deathbed by Eusebius, bishop of Nicomedia.


Christianity’s sudden change in fortune from a persecuted, outlawed sect to a tolerated and favored religion posed special problems. Christianity’s strong commitment to pacifism and its status as a religion of the lower classes were both significantly modified. The attitude of the Church toward the Roman Empire also underwent a drastic change. The seventeenth chapter of Revelation, probably written at the end of the first century c.e., is generally supposed to refer to Rome when it speaks of the woman “drunk with the blood of saints,” but Eusebius of Caesarea now saw the emperor as the vice-regent of God. Nevertheless, the dilemma had to be faced concerning where jurisdictional lines should be drawn between church and the state. Because Christians enjoyed political preferment in the imperial government after the conversion of Constantine, the Church in the fourth century was inundated with large numbers of half-convinced pagans. This mixed blessing led to early reform movements in the Church and the institution of monasticism.

The favored position of Christianity in the Roman Empire also led to a different interpretation of history. Whereas Christians during the persecutions had looked for the immediate return of Christ and the establishment of the new Jerusalem to replace the vicious rule of Rome, it now appeared that the golden age had dawned. Eusebius saw in Constantine the fulfillment of God’s promises to his chosen people through Abraham. Such a sanguine view of the state remained typically eastern; in the West, the view that became dominant was dualist in nature, seeing a constant tension between church and state.

Clearly the conversion of Constantine was a turning point in imperial and Christian history, which ultimately affected the entire Western world. Historians have variously interpreted the sincerity of Constantine’s change of heart. One view holds that his conversion was motivated by political expediency so that he might use the Church for purposes of state. The opposite position maintains that Constantine’s acts can be explained only in the light of a genuine change of heart and full conversion. A mediating position attempts to postulate a gradual change in the emperor from that of a deistic humanitarian trying to integrate Christianity with the current paganism, to one of nominal conversion by the time of his death. It should be noted that Constantine was known to place for placing great significance on dreams and visions, and one legend reports an earlier experience in which Constantine adopted Apollo as his god because of a promise that he would prosper in Apollo’s name. It is noteworthy that Apollo was linked to the Sun god, a form of monotheistic faith that Constantine seems to have adopted, perhaps preparing the ground for his conversion to Christianity, also a monotheistic religion.

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Elliott, T. G. The Christianity of Constantine the Great. Scranton, Pa.: University of Scranton Press, 1996. An examination of Constantine’s conversion and his attitude toward Christianity.
  • citation-type="booksimple"

    xlink:type="simple">Eusebius. Life of Constantine. Oxford, England: Clarendon Press and Oxford University Press, 1999. A translation of Eusebius of Caesarea’s account of Constantine’s life. Introduction, translation, and commentary by Averil Cameron and Stuart G. Hall.
  • citation-type="booksimple"

    xlink:type="simple">Grant, Michael. Constantine the Great: The Man and His Times. New York: Maxwell Macmillan International, 1994. Focuses especially on the complex religious policies and personal development of Constantine.
  • citation-type="booksimple"

    xlink:type="simple">Kousoulas, D. George. The Life and Times of Constantine the Great: The First Christian Emperor. Danbury, Conn.: Rutledge Books, 1997. A biography of Constantine the Great that focuses on his role as a converted Christian.
  • citation-type="booksimple"

    xlink:type="simple">Lieu, Samuel N. C., and Dominic Montserrat, eds. Constantine: History, Historiography, and Legend. New York: Routledge, 1998. An examination of Constantine’s life that attempts to differentiate between legend and history.
  • citation-type="booksimple"

    xlink:type="simple">Pohlsander, Hans A. The Emperor Constantine. New York: Routledge, 1996. A biography of Constantine that examines his role as Roman emperor.
  • citation-type="booksimple"

    xlink:type="simple">Reuver, Marc. Requiem for Constantine: A Vision of the Future of Church and State in the West. Kampen, the Netherlands: Kok, 1996. Reuver examines Constantine the Great’s role in the establishment of relations between church and state.
Related Articles in <i>Great Lives from History: Ancient World</i>

Constantine the Great; Diocletian; Eusebius of Caesarea. Christianity;conversion of Constantine Constantine the Great;conversion to Christianity

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