When did Constantine the Great really become a Christian?

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The Conversion of Constantine by Reubens

One of the most important figures in the ancient world was the Roman Emperor Constantine the Great. He set the stage for Christianity to become the official state religion of the Roman Empire and in doing so he not only changed that Empire but also world history. This research will discuss the evidence for Constantine's "conversion" to Christianity and identify when he can be called an actual Christian. It will focus on Constantine's alleged conversion before the t Battle of the Milvian Bridge in October, 312 AD.

There are many who have argued that Constantine did not really convert to Christianity at the time. There are those who doubt if Constantine did actually convert and that his beliefs were not those of an orthodox Christian until much later in life. The work will assert that Constantine did not have a conversion experience before the Milvian Bridge, as shown in the Christian sources and that he took many years to become a Christian.


After the Third Century Crisis, the Roman Empire had been stabilized by a series of Illyrian Emperors. Christianity at this time had been growing more popular especially in the urban areas of the Empire, despite periodic bouts of persecution. At the time of Constantine’s birth, the empire was experiencing something of a revival under the system known as the Tetrarchy established by Diocletian. During this emperor’s reign, there was a prolonged persecution of the Christians. The Tetrarchy involved several co-Emperor’s cooperating in the administration of the far-flung Empire and in the defence of its long borders.[1] This system after the death of Diocletian’s main heir, Galerius, collapsed. The co-emperors who had under the Diocletian system worked together, now fought each other for supreme power and there was a civil war throughout the Empire.

Constantine’s father had been one of the co-emperors. He had succeeded his father and was the de-facto ruler of much of western Europe. When Maxentius deposed the co-emperor in Italy, Constantine saw an opportunity to gain new territories. The Christian bishop Eusebius of Caesarea claimed that Constantine wanted to save Rome from a tyranny.[2] Constantine had advanced quickly from his base in France but his army was significantly smaller than his enemy’s. He approached Rome and camped his army before the Milvian Bridge in 312 AD.[3] Then according to Christian accounts, he had a dream or vision. The traditional account states that Constantine saw a Christian emblem in the sky. He saw this as a portent and this that led him to order his legionnaires to mark their shields with the Christian sign, the Chi Rho, similar to a cross. Lacentius relates how According to the Roman writer Lacentius Constantine ‘had marked on their shields the letter Χ, with a perpendicular line drawn through it and turned round thus at the top, being the cipher of CHRIST. [4]

Many have seen this as proof that Constantine converted to Christianity before the Battle of the Milvian Bridge. Their argument is that after his vision that Constantine became totally committed to Christianity. The next day the army of Constantine inflicted a great defeat on Maxentius and he marched into Rome, the first Christian emperor.[5] Later he defeated the ruler of the Eastern Empire and once more unified the Roman provinces under a single emperor. Constantine was a very effective ruler, he reformed the administration and rebuilt many cities, but he was an autocrat. He brought stability to the Roman empire after the civil wars and established a dynasty. Constantine also built the city of Constantinople (later Byzantium) and in doing so he laid the foundations for the medieval Byzantine Empire. His most important legacy was that he ended the persecution of Christians and legalized Christianity.[6]

Did Constantine Become a Christian?

Many such as the Christian writer Eusebius argued that Constantine’s order that his troops put a Christian symbol on their shields was proof his conversion before the Battle of the Milvian Bridge in 312 AD. However, it was usual for a leader to seek the support of a God. In the polytheism, prevalent in the Roman Empire, people would simply offer sacrificSe and thanks to the deity that they believed would be most likely to help them. Constantine’s instructions for his soldiers could be interpreted as merely seeking the support of the Christian God and not as a sign of his conversion to Christianity. Lacentius, a contemporary writer argued that because Constantine ordered his soldiers to display a Christian symbol,[7] it did not mean that he had converted. Adopting a Christian symbol was a remarkable action, given that the Roman elite scorned that religion and that most of the population was pagan.

However, Constantine had appeared to sympathize with the Christians during the persecution of Diocletian in particular. The Christian community in the west had been generally spared the worst effects of the persecution. There is a long-standing argument in the secondary literature that Constantine ‘conversion’ before the Milvian Bridge was a strategy to secure Christian support and to unify the empire. However, this is unlikely given the relative strengths of Christianity and paganism in the Empire.[8]

Paganism was not in any way in decline in the Empire during Constantine’s reign. In this context, Constantine’s alleged conversion would have been remarkable, especially given his ambition to unify the Roman Empire. The army was still largely pagan, and every Emperor depended on for his authority and even his life, on the soldiers' loyalty.[9] Then there was the Roman and Provincial nobility, who were still pagan, and every Roman Emperor needed their cooperation to control the Empire. [10] The fact that Constantine did order his legionaries to display a Christian symbol in battle is significant in the development of his religious beliefs. Because such a move was politically risky, in the context of the times when so many were pagan. This would suggest that Constantine did have some religious experience before the Milivian Bridge, even if it was not an outright conversion. Constantine’s experience in 312 AD, cannot be regarded as a conversion because it was not followed by his baptism and the public profession of that religion. In the 4th century, AD baptism was the final and public proof of conversion.

Constantine and the Church

A bust of Constantine

If Constantine did have a conversion experience before the Milvian Bridge then he would have championed the Church in the years after it. The relationship of Constantine to the Church is essential if we are to understand if he had a genuine conversion experience in 312 AD. He began immediately to favor the Christians after his victory over Maxentius. In 313 AD he reached an agreement with the Emperor in the Licinius, that ended the persecution in the eastern half of the Empire.[11]


Constantine, after 312 AD began to favor the Christian clergy and he began a large scale Church building program in Rome and elsewhere in his empire. He built Basilicas and churches, especially in Rome. Constantine promoted many Christians to important positions in his army and they were very influential at his court as advisors [12]. These could be interpreted as the actions of a new convert, who was eager to demonstrate his faith. However, there was much about Constantine that was not Christian and he was noticeably war-like, while most Christians at the time were pacifists. The Church was elevated to a position of influence but it was clearly under the control of Constantine.

This favoritism towards the Christian Church did not lead to any conspiracies or revolts and there is little evidence of any resentment from the pagan majority. Constantine was careful not to offend the significant pagan population in the Empire. In fact, at one stage the Emperor seemed to favor the worship of the Sun. This period has been glossed over by Christian writers or conveniently ignored.[13] Constantine’s policies and legislation were not explicitly Christian and he did not make it the official religion. These show that while he was very much influenced by Christianity that he was in no way an orthodox Christian Emperor, as shown in the Christian sources.

Constantine and Church Unity

A gold coin of Constantine

The Church in Constantine’s time was very divided. It was divided on theological issues and these had led to schisms in the Christian community. Constantine was to prove to be very interested in the unity of the Church after 312 AD. He held a series of Councils that was to be very important in the development of the Church and its doctrines. At these Constantine attempted to persuade the Bishops to come to an agreement on theological matters such as the nature of Christ, which was at the heart of the Arian controversy. He attempted to ensure that there were no breakaway Churches and he prevented the formation of independent Christians churches.[14]

Constantine constantly attempted to achieve unity in the Church and one that had a set of beliefs founded on the scriptures. These efforts would indicate that he had been genuinely converted at the Milvian Bridge in 312 AD. Constantine was an autocratic ruler and he attempted to impose order on every aspect of Roman life, as indicated by his administrative reforms.[15] The Christian Church was a very important part of the life of people in the Roman Empire. Its theological disputes could potentially destabilize the Empire.[16]. Eusebius portrays Egypt as ungovernable because of the theological controversies that were dividing the church in that province [17] According to Eusebius in every city ‘bishops were engaged in obstinate conflict with bishops, and people rising against people’ [18]. The deep interest that Constantine had in the unity of the Christian Church cannot be construed as indicating that he was a full professed Christian.

Constantine and Conversion

To understand if Constantine did have a conversion experience at the time of the Battle of the Milvian Bridge there needs to be an understanding of what conversion meant at the time.[19] Constantine was not technically a Christian after 312 AD, or for many years afterward, because he had not been baptized and was therefore not a full member of the Church. However, the conversion process could be gradual.[20] Constantine only seems to have slowly accepted Christian doctrine. Before this, he probably still had some lingering faith in some of the pagan deities, especially the sun-god, whose worship was very popular.[21]

Constantine was not suddenly converted to Christianity before the Milvian Bridge, but that episode was very important in his growing attachment to the Church and its doctrines. The growing relationship between Constantine and the Christian Church would indicate his growing commitment to Christianity, but that is was a long-drawn out process.[22] The ‘vision’ before the Milvian Bridge, that prompted him to order his soldiers to enter battle with a Christian sign was crucial in his early religious development. It seems that Constantine’s conversion was almost a life-long process and he was not a true Christian in 312 AD or for many years after. Indeed he was probably an old man before he was a true Christian. He only accepted baptism on his deathbed and perhaps only then could he be considered a Christian.[23]


To conclude, tradition states that Constantine converted to Christianity before the Battle of Milvian Bridge in 312 AD. Eusebius alone states that Constantine was converted and he was a Christian bishop.[24] Constantine was already sympathetic to Christianity before the Battle in 312 AD. and very gradually converted to Christianity. He did not receive baptism until just before his death. A prolonged conversion process was typical of the period and it was only with the onset of death that the emperor could convert. It would have been very difficult for him to rule a largely pagan population if he had become a full member of the Church. Constantine did not convert in 312 AD, but the vision of Constantine, before the Battle of the Milivian Bridge was an important stage in his eventual conversion to Christianity. It can be said with some confidence that Constantine the Great was a life-long supporter of Christianity but did not actually become a fully committed Christian until his baptism shortly before he died.


  1. Cameron, A. The later Roman Empire, AD 284-430 (Cambridge, Mass.: Harvard University Press. 1993), p 56
  2. Eusebius, xviiii
  3. Cameron, p 113
  4. Lactantius, De Mortibus Persecutorum Chapter XLIV
  5. Lactantius. X,IV
  6. Cameron, p 114
  7. Lacentius XIV
  8. Roth, J. (2013). Constantine revisited (London, Wipf & Stock Pub, 2015), p. 67
  9. Cameron, p. 104
  10. Cameron, p. 102
  11. Drake, H.A., "The Impact of Constantine on Christianity", in Lenski, N (ed.), The Cambridge Companion to the Age of Constantine, Cambridge, 2006: 111-136
  12. Drake, 2006, p. 121
  13. Cameron, p 115
  14. Eusebius, VI
  15. Cameron, p 112
  16. Rapp, C., "Imperial Ideology in the Making: Eusebius of Caesarea on Constantine as Bishop", Journal of Theological Studies, 49 (1998): 684-95
  17. Eusebius, IV
  18. Eusebius, Vita Constantini. Vi
  19. Rapp, p. 65
  20. Elliot, Thomas G., 'Constantine's Conversion; do we really need it?' Phoenix 41 (1987), 420-438
  21. Elliot, p. 430
  22. Smith, M.D., "The Religion of Constantius I", Greek, Roman and Byzantine Studies 38 (1997): 187-209
  23. Smith, p. 189
  24. Eusebius, Vita Constantini. Vi