Why Did Constantine the Great Choose Christianity?

What could be the rationale and motivations behind Constantine’s choice to convert to Christianity rather than to subscribe to the Cult of Sol Invictus or Apollo?

Apr 5, 2023By Cameron Hughes, MA Field Archaeology, MA Politics

jesus crucified constantine the great saint painting


The conversion of the Roman Emperor Constantine the Great, and subsequently the whole Empire, is seen as a historical watershed moment in Roman history. The nexus from which the classical world of polytheistic pagan Rome began its transition to the medieval world of monotheistic Christianity and Islam. In many ways, this portrayal is accurate, as prior to his conversion, the Christian population was only around 5% of the Empire’s total, 3 in 60 million estimated. Meaning that without the patronage of Constantine, the early church could have remained an eastern cult of the urban poor. However, Constantine’s conversion was the culmination of a greater trend toward divine legitimacy among the rulers of the ancient world. This article will explore how this trend developed over the course of centuries and try to determine why, from a number of options, Constantine chose the Christian faith.


The Imperial Cult: Before Constantine the Great Had Chosen Christianity

“In Hoc Signo Vinces”, Statue of Constantine the Great outside York Minster, York, England, via Learn Religions.


The fledgling Roman republic had expelled the last of its 7 Kings in 509 BCE. Henceforth the political system was orchestrated to divide and constrain the power of any individual. The executive power and military command of this republican system were split between two Consuls, each serving 1-year terms. Throughout this period, the Roman Pantheon of gods flourished and adopted new deities into its systems of belief, as the Roman world expanded to dominate the Mediterranean basin. Following nearly two decades of upheaval in the civil wars (49-31 BCE), political power in the Roman Republic was consolidated under the sway of a single man, Augustus. His authority began the phenomenon of the imperial cult. The state-ordained authority of the emperor awed the Roman people with its scale and reach and upon his death, Augustus was apotheosized by the senate and voted divine status as a Roman God.


Alexander The Great, From The Alexander Mosaic in Pompeii, c. 100 BCE, via Wikimedia Commons


The conflation of mortal man and divine being was not a novel idea of the Augustan age. Unknown to the contemporary Romans, the Chinese and Japanese had divine emperor deities. Closer to home, the Egyptians had worshipped their Pharaohs as living gods before the Ptolemaic dynasty. The Ptolemies had instead used the Hellenic imperial cult of Alexander the Great as their cornerstone of legitimacy, a legacy respected by the Romans as well. The Hellenes, too, had a long tradition of merging the mortal and divine. The gods of the Greek pantheon were known to meddle in the affairs of men and to sire half-divine half-mortal children such as Heracles and Perseus. It seemed that wherever power was concentrated or abilities unmatched, an aura of divinity would be cast upon mortals as the rationale for their unique circumstance or exceptional achievement.


The 3rd Century

Wedding Banquet of Cupid and Psyche, showing the major Roman gods, by Raphael, c.1518, via Wikimedia Commons

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This trend of apotheosis was continued in Rome after Augustus for respected emperors and members of the imperial family. Few emperors chose to rule as living gods, notably Caligula and Domitian. This was a step too far for much of the Roman elite, who preferred their ruler to be a first citizen rather than a divine superior. Emperors achieving divine status would find their dynastic heirs afforded a legitimacy that masked their individual shortcomings for a time, notably in the cases of the Flavian and Severan bloodlines. The penultimate ruler of the Severan line was imported from the Eastern Syrian provinces. Elagabalus attempted to replace Jupiter, the head of the Roman Pantheon, with the Eastern Sun God, Elagabal, of whose cult he was the high priest. His religious peculiarities, compounded with his sexual degeneracy, led to his assassination in 222 CE, aged 18.


Crisis of the Third Century, map of emperor’s deaths, via Vox


By now, the veneer of the semi-consensual principate designed by Augustus was giving way to a more blatant exercise of political and military authority, which would come to be known as the dominant. The 3rd century was dominated by political crises and civil wars as the legitimacy of the principate came under strain while the burden of such a vast empire became apparent. As the strength and legitimacy of the emperors teetered, the religious cults of the Empire grew throughout the 3rd century. The citizens of the Empire began more than ever to put their faith in Sol Invictus, Mithras, and Christ, spurning the traditional pantheon endorsed by the Roman elite and seeking moral philosophy and religious authority as one.


Philosophic and Religious Cults in the Roman Empire

The School of Athens by Raphael, c. 1509-11, via Musei Vaticani, Vatican City.


The Mediterranean world contained a rich abundance of religious deities and philosophic schools of thought. Each province, and even each city, would bring new beings into the Roman Pantheon, while the academy at Athens and dozens more schools across the Empire churned out graduates in philosophy and rhetoric each year. After its incorporation into the Empire, Greece, with its philosophic traditions, began to filter into mainstream Roman culture, appealing to the philhellenic segments of the Roman aristocracy. By the 2nd century, two main schools of thought were prominent in Roman society, Stoicism and Epicureanism. At the same time, the exchange of cultures along the Empire’s vast road and trade networks introduced oriental cults to the hills of northern Britain and allowed the Roman pantheon to flourish on the plains of Syria and Egypt. Though the emperor retained the title of Pontifex Maximus, he was not a spiritual leader in the same sense as the modern Pope, more a ritualistic figurehead.


Head of Emperor Tiberius, 4-14 CE, via British Museum


Throughout the first few centuries of this imperial project of cultural osmosis, the religious beliefs and the moral philosophies of the peoples under the Roman Empire remained separate. However, these two aspects of daily life, combined with the prevalence of belief in the potential divinity of mortal men, meant that it would only be a matter of time before a philosophic leader would accrue a cult-like following and divine status. During the reign of Augustus’s designated successor, Tiberius (14-37 CE), a Jewish carpenter in the Eastern province of Judaea gathered a small following to his teachings of love, peace, and forgiveness. His teachings were largely compatible with the Jewish faith, except for one claim. That this philosophic carpenter, Jesus, was the son of God.


Early Christianity

Jesus crucified by the Romans in Jerusalem, by Harry Anderson, via Church of Jesus Christ


This claim of divine lineage was unacceptable to the Jewish community of Judaea, who petitioned the Roman governor, Pontius Pilate, to label Jesus a dangerous rebel. The province had only recently been annexed and was clearly a tinderbox of social and religious quarrels. Pilate had Jesus arrested and executed by crucifixion. This would have been the end of another Eastern pop-up cult had reports not surfaced that Jesus had revived three days after his death. As it would come to be known, this’ resurrection’ was the advent of the Kingdom of God and the proof that all mankind could be absolved of sin and reborn again after death. When news reached Tiberius of this miracle, he enquired as to whether the senate believed that Jesus should be voted into the Roman Pantheon of Gods alongside Jupiter and Mars. They refused.


The original disciples of Jesus Christ, the apostles, spread throughout the Roman world and dispersed the teachings of Christ. They were initially only received by slaves and the poor as their message of charity and loving thy neighbor was ill-met by the wealthy. For all intents and purposes, the Roman elites continued to view them as an offshoot sect of the already bizarre monotheistic Jewish faith. In the 2nd century, they were seen as annoying fanatics desperate to die for their God. By the 3rd century, they had become a notable grouping and were the targets of several persecutions. The growth of such a small sect was remarkable, with modern observers compiling several mathematical models to try and explain it, though by and large, the Roman Pantheon remained the core belief of the Roman world. This would soon begin to change with the rule of Constantine.


3rd Century Attempts at Divine Legitimacy

Coin minted in the reign of Aurelian bearing both him and Sol Invictus, via Coin Talk


After Elagabalus’ failed attempt to leapfrog his patron deity to the head of the Roman Pantheon, the Roman world was dominated by 50 years of civil conflict. During this, the emperor Decius attempted to persecute the growing Christian cult, and other substantial cults emerged, such as those of Mithras and Sol Invictus. The crumbling Empire was reunified by the soldier-emperor Aurelian (270-275 CE), who began to style himself as dominus et deus (Master and God) under the cult of Sol Invictus, a relation of Elagabal, which gained first place in the Roman Pantheon. It must have seemed clear to Aurelian that his exceptional abilities as a general and emperor resulted from his relationship with the unconquered sun, therefore granting him political legitimacy and qualifying Sol as the principal deity of Roman religion. Aurelian was assassinated by his troops for matters unrelated to his religion.


Not long after Aurelian, Diocletian became the master of the Roman world. As part of his diarchic and tetrarchic systems of government, he styled himself, and his imperial colleague Maximian, as Iovius and Herculius (Jupiter and Hercules). This established the Roman emperors as gods among men. This was an attempt to establish a divine legitimacy that could not be sourced from any dynastic claim, therefore dissuading any potential usurpers through sheer awe. It worked as Diocletian was able to remain in power for 20 years, chose to retire, and was begged to retake the throne after his departure by his former colleagues. Here we see, in the decades preceding Constantine’s ascension, an increasing tendency to seek legitimacy as ruler from a divine authority after the ruin of the dynastic methods of the pre-3rd century.


Constantine’s Quest for Legitimacy 

Constantine’s vision of the cross, by Raphael, via Vatican Museums


The life of Constantine was a dramatic and eventful one. He reigned for more than 30 years, eliminating all his rivals, and laying the foundations for a Christian empire and the city of Constantinople, which outlived him by more than a millennium. But, early in his reign, he was but one of 6 self-proclaimed Augusti in the imperial college, all seeking to establish their legitimacy as Roman emperors. Even though he was the son of a former Caesar, Constantius, and had proved himself a capable general and leader of men, Constantine knew he would need a further layer of legitimacy if he was to establish a lasting dynasty.


Constantine’s propagandists initially claimed (310 CE) he was the adoptive heir of Emperor Claudius II Gothicus; one of the few well-remembered and, more importantly, deified rulers of the dark 3rd century. As an obvious fabrication, this was readily ignored. In 312 CE, he defeated the forces of Maxentius at the Milvian Bridge north of Rome itself. This victory left Constantine in possession of the entire Western Empire and allowed him to claim divine favor for his cause, establishing a unique legitimacy. Constantine was an open-minded young man who had received a liberal education and traveled far and wide. Resultingly, he kept several different personalities at court, including some Christians. However, this did not necessarily mean that his conversion to the faith of Christ was assured.


Constantine’s Choice

Christ as the Sun God, in Tomb of Julii (Mausoleum “M”) in the Vatican necropolis, 3rd century CE, Rome, via flickr


Preserved in Panegyric VI (21) of the Panegyrici Latini, Constantine supposedly witnessed a vision of the God Apollo en route to the Milvian Bridge. Apollo presented himself in one of his glorious temples to Constantine and offered him divine ordination, the laurel crown, and 30 years as ruler of the Roman world. All this is because of Constantine’s likeness to the Sun God. In return, Constantine would need to expand the worship of and sacrifice to this deity.


As well as Apollo, Sol Invictus, the Unconquered Sun, was associated with Constantinian propaganda. Constantine had adopted Sol as a personal deity by the latest 305 CE and continued to mint coins bearing the Sun deity until 319 CE, seven years after his victory at the Milvian Bridge. Sol had been used in attempts by Claudius II and Aurelian to move the Empire towards a monotheistic god behind a single emperor as a political expedient to prevent continual usurpation and civil war. It seems that Constantine had initially proceeded in their footsteps but had, at some point, decided to merge the Unconquered Sun with Jesus Christ as his patron deity.


Constantine’s victory at the Milvian Bridge 312 CE, Raphael & Giulio Romano, 1520-25, via Vatican Museums


Both the sabbath, Sunday (day of the sun), and Christmas day derive from practices and observances in the cult of Sol Invictus. The cult of the Sun God also promoted absolving sins, rebirth, abstinence, resurrection, monotheism, and a form of baptism. Constantine recounted to Eusebius (1.29) his vision of the Cross appearing in the light of the sun with the instruction ‘In Hoc Signo Vinces’, by this sign conquer. Other reports claim different visions, and it is likely that Eusebius, a Christian, had convinced Constantine that this was a sign from the Christian God. The solar signal is also reported to have presented the Greek letters Chi and Rho to Constantine, the first two letters of Christos, and therefore another sign of the Christian God. Though the Chi-Rho has also been associated with Kronos, Saturn, a disciple of Sol.


Ultimately, though it is likely that Constantine did witness some sort of solar phenomenon prior to his battle at the Milvian Bridge, it is just as likely that the accounts we have been handed through history have been subject to misinterpretation and revisionism. Though he may have initially interpreted the sign as the support of Sol Invictus, Christian advisors likely convinced Constantine that it was their God who protected him. This would explain the continued minting of coins in the name of Sol until 319 CE and the gradual amalgamation of the calendars and practices of the Christians and the Unconquered Sun.


Why Christ?

The Saints Constantine the Great and Helena, by Athanasie Wallachia, 1699, via the National Museum of Art of Romania, Bucharest


The Empire had seen the collapse of dynastic legitimacy after the Severans in the early 3rd century. At the end of the 3rd century, Emperors had begun experimenting with establishing legitimacy through the ‘one god, one emperor’ model. Diocletian had successfully styled himself as a Godlike emperor, though he had operated through the lens of the traditional Roman pantheon. Constantine seems to have sought to establish his legitimacy through monotheistic means. Elagabalus, Claudius II, and Aurelian had all toyed with the idea of Sol Invictus as their ‘one god’ and Constantine also had close familial connections and sympathies to this cult.


It was also apparent that, as one of the most powerful men in the Empire, Constantine would be approached by all sects attempting to seduce him for their cause. He remained open-minded, keeping an open and fluid court. Traditional Roman polytheists must have attempted to lure him toward Apollo, though he would have known that continuing with the traditional pantheon would leave him open to assaults on his legitimacy. Sol seemed promising, though had already been tried and failed on three occasions. Sol was also already very popular among the Roman elite and so could be used as a divine patron for another powerful Roman seeking to claim the imperial throne.


The Christian sect remained relatively small, though not insignificant, had an empire-wide following, though not among his fellow elites, and preached peace and pacifism. As a doctrine, it would serve him well by revolutionizing Roman religion, allowing him to reconstruct society as a new founder of Rome, rewarding loyal converts to his doctrine and identifying potential pagan rivals more easily. Also, it would allow him to pacify a martial and restless population, directing their energies toward worship instead of war. All of these were reasons to favor the Christians, but most importantly, it was a monotheistic creed, placing all the powers of one God behind Constantine’s rule. To a deeply religious populace, this would make his sovereignty unquestionable. It also raised the question as to whether Constantine himself was a devout Christian or simply acting pragmatically?


So, Why Did Constantine the Great Choose Christianity?

The reach of Christianity up to and following Constantine’s conversion, via Vox.


Constantine’s conversion and 30-year rule of the Roman Empire can be seen as the culmination of religious, philosophical, and political trends spanning centuries. The ancient belief in apotheosis and the relationship between mankind and the gods, the spread of philosophic schools of thought, and the need for divine political legitimacy after the upheaval of the 3rd century. Combined, these factors led to Constantine’s momentous decision to convert to Christianity and promote it as the sole religion of the Empire in his later life. Though he did not officially convert until just before his death, remaining a catechumen most his life, his eventual conversion changed the world forever.

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By Cameron HughesMA Field Archaeology, MA PoliticsCameron is a contributing writer with an interest in the transitional period between late antiquity and the early Middle Ages in Europe. He holds an MA in Field Archaeology from the University of York, and an MA in Politics from the University of Birmingham. His Masters dissertations have been on the end of Roman Britain and the concept of ‘crisis centuries’ in Western history.