Why did Roman Emperor Constantine the Great convert to Christianity?

Why and when did Constantine the convert to Christianity?

Constantine the Great’s decision to become a Christian was massive and forever changed the course of the Roman Empire and human history.

After more than three centuries of ruthlessly persecuting Christians across the empire, the Roman Emperor witnessed a huge change. Emperor Constantine the Great (reign: 306-337) broke away from his predecessors’ intolerant attitude towards Christianity and converted to Christianity.

What influenced his decision? Was it out of political expediency or did it have to do with some genuine spiritual vision or awakening? And how did the emperor’s conversion to Christianity impact the Roman Empire and the rest of history?

Below, World History Edu provides a detailed explanation of why Constantine the Great put aside his polytheistic pagan beliefs and accepted the teachings of Jesus Christ.

Rome’s long history of deifying their rulers

Typical of many ancient kingdoms and empires, the Roman Empire as well as its predecessor the Roman Republic, had the habit of deifying their rulers. For example, after the assassination of Julius Caesar in 44 BC, his supporters, led by his heir and grandnephew Octavian (later Emperor Augustus), saw to it that the former dictator was voted a god.

The process of deification involved a series of rituals and ceremonies that were meant to elevate Caesar to the status of a divine being. It began with a public funeral and the construction of a temple in Caesar’s honor. The Senate also declared him to be a god, and his image was placed on Roman coins alongside images of some Roman gods, especially deities of his family cult.

Caesar’s deification was an important political and cultural event in ancient Rome. It helped to legitimize Octavian’s claim to power and establish the idea of the Roman emperor as a god-like figure. It also reflected the growing importance of religion and ritual in Roman society, as well as the close association between political power and religious authority.

And so the practice of having an imperial cult emerged as successive rulers of the Roman Empire got elevated to divine status, especially after their deaths. It was also the case that some of members of the imperial family could attain divine status, especially if that person distinguished him/herself. A good number of the Julio-Claudian dynasty (i.e. family of the first five Roman Emperors – Augustus, Tiberius, Caligula, Claudius, and Nero) members were deified.

Read More: 10 Greatest Achievements of Augustus, Rome’s First Emperor

Did you know…?

In some cases, the Roman emperors did not wait until their death before receiving divine status. The likes of Caligula (reign: 37-41), Domitian (reign: 81-96) and even Elagabalus (reign: 218-222) asaw themselves as living deities.

Rationale for the deification of Roman rulers

In the ancient world, it appears that wherever absolute power went, some kind of divine status was conferred on the holder. What this means is that political power and religious authority went hand-in-hand. It was perhaps the people’s explanation of the brilliance, strength, affluence, and sheer royalty of their rulers.

To the Romans, there simply wasn’t any other logical explanation for the bravery and fearlessness exhibited by someone like Julius Caesar or Emperor Claudius. Surely, those people must have had some kind of divine traits in them in order to chalk up those spectacular feats

It was also very important for the deceased Roman ruler to be elevated to divine status as it in a way legitimized the reigns of their dynastic heirs. If a Roman Emperor is perceived as the son of god, then he simply could not do anything wrong, making the power he wielded nothing short of absolute.

Sol Invictus

Coin of Roman Emperor Marcus Aurelius Probus (reign: 276-282) depicting Sol Invictus (also known as the Unconquered Sun) riding a quadriga

Rome’s Crisis of the 3rd Century

Starting around the third century AD, Rome found itself rocked by a series of unsavory political, economic, social and military events. Known as the Crisis of the Third Century, the political instability spanned from 234 to 285. It created a revolving door of emperors. For example, in just that 50-year period, the Romans witnessed a staggering 24 emperors. Basically, Rome, a vast empire, appeared to be on the edge of implosion as wars and succession crisis became the order of the day.

Crisis of the Third Century

The crisis only came to an end when Diocletian (reign: 284-305) came to power in 284, at which point he proceeded to divide the empire into the eastern and western part.

The crisis led to a number of significant changes in the Roman Empire. The military was reorganized and new administrative systems were put in place to try to restore stability. The power of the Senate was diminished, and the emperor became more powerful. The empire also began to decentralize, with regional governors gaining more autonomy.

It’s important to note that the crisis coincided with the rise in the religious cults in the empire, especially the ones related to the worship of deities like Mithras, Sol Invictus and Apollo.


Roman emperors elevate themselves to the status of living gods

As the Crisis of the Third Century unfolded, some Roman emperors strived to gain political legitimacy by presenting themselves as gods. Following in the footsteps of Elagabalus, Roman Emperor Aurelian (reign: 270-275) took the epithet “dominus et deus”, which means “Master and God”.

Similarly, Emperor Diocletian and his co-emperor Maximian called themselves Iovius and Herculius – Jupiter and Hercules, respectively. No longer would they derive political legitimacy from only blood lines and dynastic links; but, they sought it by making themselves divine.

The Growth of Christianity in the Second and Third Centuries

Following in the footsteps and the instructions of Jesus, early Christian leaders journeyed across the empire, carrying with them the message of love, brotherliness and charity. As a result, their message was well-received by downtrodden masses and citizens of the Roman Empire.

In the 2nd and 3rd centuries, the wealthy Roman citizens and elites continued to perceive Christians as huge threats, and therefore intensified the persecution of them. Christians, on the other hand, were not one bit perturbed by the stones thrown at them as many believed that there was no greater display of one’s devotion to God than getting martyred.

Saint Lawrence was martyred in the persecution of the Christians that the Roman Emperor Valerian (reign: 253-260) ordered in 258.

Contrary to what the Roman elites forecasted, Christianity continued to grow in leaps and bounds. Christianity, a small religious sect that emerged in Judea, became very popular among the urban poor in the Roman Empire.

By the start of the fourth century, Christians made up about 5% of the population of the empire. That figure translated to between 2.5 and 3 million of Rome’s 60 million population.

During the Crisis of the 3rd Century, the early Christian church had made tremendous progress and impression among the urban poor across the empire.

Reasons why Constantine chose Christianity

In the decades that followed after the Crisis of the 3rd Century, it became apparently clear that Roman emperors needed to go beyond associating themselves with a god and being gods – they had to find their legitimacy from a ‘true’ god. One such Roman emperor was Constantine the Great (reign: 306-337).

Born in 272, Constantine came to be known for his military successes during a power struggle that followed the death of his father, Emperor Constantius Chlorus (also knwn as Marcus Flavius Valerius Constantius) in 306 AD.

He defeated about five other rivals in the imperial college and became the sole ruler of the western portion of the empire. He also defeated the forces of Maxentius at the Battle of Milvian Bridge in 312 AD, which is said to have been a turning point in his career and ultimately led to him becoming the sole ruler in the West.

In his attempt to further boost his legitimacy, Constantine realized that being the son of former Caesar was not going to cut it so to speak. This explains why he claimed he was the adoptive heir of Emperor Claudius II Gothicus (reign: 268-270), a Roman ruler who was admired for his military campaigns against the likes of the Goths, the Palmyrenes, and the Alamanni.

When that dynastic claim failed to give him the legitimacy that he desired, he claimed that he had some sort of divine favor, which was evident in his famous victory over Maxentius at the Milvian Bridge in 312.

After converting to Christianity, Constantine began the gradual Christianization of the Roman Empire. Image: Head of the Colossus of Constantine, Capitoline Museums in Rome, Italy

Constantine’s fascination with Apollo and Sol Invictus

It is likely that Constantine was influenced by his father’s policy of reconciliation with the Christian population of the empire. This explains why some of his senior officials were Christians even though he himself was not a Christian. Rather, he was ardent follower of the Roman god Apollo. According to him, Apollo appeared to him on his way to Milvian Bridge.

Constantine also worshiped another sun deity known as Sol Invictus. The Roman god was known as the “Unconquered Sun”. The cult of Sol Invictus emerged during the reign of the emperors Claudius II and Aurelian (270-275 AD) and was intended to unify the various religious traditions of the empire.

The cult of Sol Invictus was a syncretic religion that blended elements of various other religions, including traditional Roman religion, Mithraism, and the worship of other eastern deities. Sol Invictus was often depicted as a sun god, riding in a chariot and holding a globe that represented the sun. He was also depicted with the solar crown of rays.

It is known that Constantine was a patron of the arts and architecture, and he sponsored the construction of a number of impressive buildings and monuments, including the Basilica of Maxentius and the Arch of Constantine. Some of these buildings may have featured depictions of Sol Invictus or other sun gods.

Jugate gold multiple issued by Constantine at Ticinum in 313, showing the emperor and the god Sol, with Sol also depicted in his quadriga (chariot) on Constantine’s shield.

Constantine most likely caught on to the attempts by Claudius II and Aurelian to develop some kind of monotheistic religion with Sol Invictus as the only god. He also realized that a monotheistic religion could be the source of what he had been searching for a long while – i.e. long-lasting political legitimacy.

Sol Invictus

Sol Invictus, which means “Unconquered Sun” in Latin, was a Roman god who was worshiped from the late 3rd century AD to the 4th century AD.

Therefore, Constantine took the bold decision to merge Sol Invictus with Jesus. The latte seemed like a reasonable choice as he was the leading figure to many of his Christian courtiers.

For example, it is likely Constantine was the one who began celebrating the birth of Jesus on December 25 (i.e. Christmas). Interestingly, that day occurred during the festival of Saturnalia was celebrated. As a matter of fact the birthday of Roman sun deities Sol Invictus and Mithras both fell on December 25.

Parallels between Sol Invictus and Jesus Christ

Similar to followers of Jesus Christ, followers of Sol Invictus believed in the concept of rebirth, the absolving of sins, and resurrection. The event that further cemented the link between Sol Invictus and Jesus Christ came when Constantine claimed that he had a vision of the Cross appear in the light of the sun.

It is said that emperor either had a dream or vision on the night before his famous battle against rival Maxentius in 312. There was also a script in the background that read “In Hoc Signo”, which means “In this sign, conquer”. After his victory over Maxentius, the emperor and his court officials, many of whom were leaning to Christianity, would interpret the vision as sign from the Christian God.

In the vision that Constantine the Great had, he claimed to have witnessed the Cross in the background of a bright light coming from the Sun.

Constantine the Great is believed to have had a vision before the Battle of the Milvian Bridge in Rome in 312.

The emperor made this revelation known to Eusebius of Caesarea (260-339), a Christian historian and theologian best known for works such as “Ecclesiastical History” and “The Life of Constantine”. Eusebius’ works had a significant influence on the development of Christian thought and theology.

Some historians maintain that Eusebius managed to convince the emperor that the vision came from the Christian God and not Sol Invictus. Further interpretation of the vision was made by Eusebius to reinforce the first assessment.

Regardless, Constantine continued to maintain his devotion to Sol, offering sacrifices to the Roman god. There was considerable effort from the Emperor to merge the two beliefs – Sol and the Christian God.

Eusebius of Caesarea

In addition to his “Ecclesiastical History,” Eusebius wrote a number of other influential works, including “The Life of Constantine,” a biography of the first Christian emperor, and “The Preparation of the Gospel,” which sought to demonstrate the compatibility of Christianity with classical Greek philosophy. Today, he is remembered as one of the most important figures in early Christian history and theology. Image: 6th century Syriac portrait of St. Eusebius of Caesarea from the Rabbula Gospels

Constantine’s Edict of Milan – the edict of toleration that proved to be a game changer

The Edict of Milan was a proclamation issued by Roman Emperors Constantine and Licinius in February 313 AD. The two Roman leaders met in Mediolanum (modern-day Milan) and issued a proclamation that granted religious toleration to all religions, including Christianity, throughout the Roman Empire. The Edict of Milan effectively curtailed the persecution of Christians, which had been taking place sporadically since the reign of Emperor Nero in the first century AD.

In spite of the persecution of Christians intensifying all throughout the 2nd and 3rd centuries, Christianity continued to make huge gains. In  In the early 4th century AD, Christians made up about 5% of the population of the empire. That figure translates to between 2.5 and 3 million of the 60 million population. Image: Triumph of Faith by Eugene Thirion (19th century) depicts Christian martyrs in the time of Nero

The proclamation was significant because it recognized Christianity as a legitimate religion and allowed Christians to openly worship and practice their faith without fear of persecution. It also allowed Christians to reclaim their property and granted them the right to hold public office, which had previously been denied to them.

It must be noted that some competing Roman generals and politicians for the throne of Rome in the second and third centuries AD had the habit of issuing edicts of toleration in an attempt to secure the support of persecuted Christians. The likes of Galerius of the Eastern Empire (reign: 305-311) who was a known persecutor of Christians made a U-turn and issued an edict of toleration in order to recruit Christians into his legions.

Co-authored with Emperor Licinius, the Edict of Milan was issued in 313 to grant Christians the same legal rights as worshippers in the hundreds of religious cults that existed in Rome at the time. Image (L-R): Roman Emperors Licinius and Constantine the Great

Long-lasting political legitimacy through monotheism

Having defeated his colleague emperor Licinius (reign: 308-324) in 324 (at the Battle of Chrysopolis), Emperor Constantine, who was now sole ruler of all the empire, set out secure a long-lasting legitimacy that would be free from any questioning. Some scholars say that he did this by casting his lot with monotheism.

Constantine had witnessed how his predecessors, despite styling themselves with divine statuses, had their legitimacies challenged. The emperor reasoned that as Christianity was a monotheistic religion, his legitimacy would go uncontested since he served an all-powerful god.

He also hoped to make good use of the message of peace and love that the Christians preached to bring back some stability and harmony to an empire that was plagued by political and economic instability in the previous century.

Taking cues from the policies of Emperor Aurelian, Constantine desired to have one emperor and one church, with both deriving their powers from one god. Image: The Baptism of Constantine, as imagined by students of Raphael

Did Constantine the Great indeed became a Christian because he wholeheartedly believed in the Christian God? Or did he become a devout follower of the Christian God because he believed that Christianity gave him a long-lasting political legitimacy – i.e. a kind that could not have been obtained from other Roman gods?

And with Christians making up about 5% of the population during the reign of Constantine, it is likely that emperor had the foresight that Christianity would go on to be a dominant force in the empire. This is also another possible explanation of why Constantine decided to cast his lot with the Christian God.

There are some historians that claim that Constantine’s mother, Helena, was a Christian before Constantine converted to Christianity. If that were the case, then the emperor did not need a lot of convincing to embrace the Christian God.

Did you know…?

It was not until his final few moments did Constantine let himself be baptized as a Christian.

Interesting facts about Constantine’s conversion to Christianity

Some scholars have described Constantine as the bridge between the classical world of polytheistic paganism and the medieval world of monotheistic Christianity and Islam. Image: Eastern Orthodox Bulgarian icon of Saint Constantine and his mother Saint Helena

Even after the issuance of the Edict of Milan in 313 AD, Constantine continued for some time to depict himself on coins along with Roman deities like Apollo and Diana.

The Edict of Milan did not mean that Constantine was committed Christian as other religious cults in Rome continued to go on uninterrupted.

It was after the Council of Nicaea in 325 that Christian Emperors began depicting themselves with the halo symbol over their heads. This symbolized that the Roman emperor was the representative of Christ on earth. The Council of Nicaea was a meeting of Christian bishops in 325 AD that affirmed that Jesus was fully divine and of the same substance as God the Father.

One Constantine became the patron of Christians, he had a number of Christian images, including the cross, placed on the military gear of his legions. In fact, it was Constantine who made the cross a very popular Christian symbol.

During her trip to Jerusalem in the East, Constantine’s mother, Helena, believed that she discovered the “true cross”. Upon hearing the news, Constantine ordered the construction of a number of religious buildings – including The Church of the Holy Sepulcher and The Church of the Nativity in Bethlehem.

Constantine is also credited with building the first basilicas of St John in Lateran and St. Peter in Rome. In his new capital city, Constantinople, the Emperor built the Church of the Holy Apostles.

It was not until 381 that Roman Emperor Theodosius I (reign: 379-395), a strong adherent to the Christian faith, outlawed the old state cults and other religious cults. The decision marked the official Christianization of the Roman Empire. As Christianity became a religion promoted by the emperors, any criticism of the religion was deemed treason.

It was not until a few moments before he died that he was baptized as a Christian. Some historians have argued that this is further proof that Constantine was not 100% committed to Christianity in his lifetime.

Church of the Holy Sepulchre in the Christian Quarter of the walled area in East Jerusalem


Constantine’s conversion had a profound impact on the history of Christianity itself. It paved the way for the development of a powerful Christian Church that would play a major role in European and world history. Without Constantine’s conversion, it is possible that Christianity would have remained a relatively small and persecuted religion, rather than the dominant faith of the Western world.

How did Constantine’s vision at Milvian Bridge facilitate the spread of Christianity?


Brown, Peter. The Rise of Western Christendom: Triumph and Diversity, A.D. 200-1000 (10th ed.). Wiley-Blackwell, 2013.

Brown, Peter. Through the Eye of a Needle Wealth, the Fall of Rome, and the Making of Christianity in the West, 350-550 AD. Princeton University Press, 2013

Burckhardt, Jacob & Hadas, Moses. The Age of Constantine the Great. University of California Press, 1983.

Cowen, Ross. Milvian Bridge AD 312: Constantine’s battle for Empire and Faith. Oxford, UK: Osprey Publishing, 2016.

Elton, Hugh. The Roman Empire in Late Antiquity A Political and Military History. Cambridge University Press, 2018.

Leithart, Peter J. Defending Constantine The Twilight of an Empire and the Dawn of Christendom. InterVarsity Press, 2010.

Potter, David. Constantine the Emperor. Oxford University Press, 2012.

Robin Lane Fox. Pagans and Christians. HarperCollins, 1988.

Schaff, Philip. Nicene and Post-Nicene Fathers. Cosimo Classics, 2007.

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