Constantine — did he invent Christianity?

Ask almost any sceptic where Christianity came from and, sooner or later, the name Constantine will come up.

The story goes something like this: a Roman emperor, for political reasons, took a scattered movement, voted its teacher into a god, selected the books he liked for a new Bible, swapped the Sabbath for the sun's day, and forced the result on his empire.

It is a neat story. It is repeated by readers of The Da Vinci Code, by some Muslim apologists, by Jehovah's Witnesses, by people in Sabbath-keeping groups, and on countless social media pages. And it gets almost every detail wrong.

Constantine was enormously important. But to see what he actually did, you have to put the events in the right order.

The church Constantine found

By the time Constantine came to power, Christianity was nearly three hundred years old.

It had its Scriptures. During the Great Persecution of 303–311, the emperor Diocletian ordered Christian books to be handed over and burned — you cannot burn books that do not exist. Gospel manuscripts such as P66 and P75 were copied around AD 200. Writers like Irenaeus around AD 180 already treated four Gospels as the church's settled set.

It worshipped Jesus as God. Ignatius of Antioch, on his way to martyrdom around AD 110, called him "Jesus Christ our God". The Roman governor Pliny reported around AD 112 that Christians sang hymns "to Christ as to a god". A third-century prayer hall at Megiddo in Israel has a floor mosaic dedicated "to God Jesus Christ" — dated by its excavators to the third century, though some scholars place it later.

And it was large. Historians such as Rodney Stark estimate that perhaps a tenth of the empire was Christian by AD 300, after three centuries of being illegal. Constantine inherited a movement that the most systematic persecution in Roman history had failed to destroy.

The Milvian Bridge, AD 312

In 312 Constantine was one of several rival emperors fighting for control of the Roman world. He marched on Rome against his rival Maxentius and met him at the Milvian Bridge over the River Tiber on 28 October.

Before the battle, something happened. We have two Christian accounts of it, and they do not quite agree.

Lactantius, a Christian teacher at Constantine's court, writing a few years later, says Constantine was told in a dream to mark the heavenly sign of God on his soldiers' shields — a monogram formed from the first letters of Christ's name in Greek.

Eusebius, bishop of Caesarea, writing after Constantine's death, says the emperor told him personally, on oath, that he and his army saw a cross of light in the sky above the sun with the words "By this, conquer", followed by a dream in which Christ explained the sign.

Constantine won. Maxentius drowned in the Tiber. And Constantine attributed his victory to the God of the Christians.

Historians debate what lay behind the accounts. Some think Constantine saw an unusual solar halo; a pagan speech from 310 had already described him seeing a vision of the sun god Apollo. What is not in doubt is that from this point on Constantine publicly identified himself with the Christian God.

The "Edict of Milan", AD 313

The following year Constantine met his fellow emperor Licinius at Milan. They agreed a policy, published as a letter by Licinius, that is usually called the Edict of Milan.

It is worth reading what it actually did. It granted freedom of religion to everyone, Christians and pagans alike, and ordered that church buildings and property seized during the persecution be returned. It did not make Christianity the state religion. It did not outlaw paganism.

That point is easy to lose. For most of his reign Constantine ruled an empire that was still mostly pagan, and he kept the old pagan title of Pontifex Maximus, chief priest. His coins continued to show the Unconquered Sun until the early 320s. The triumphal arch the Senate built for him in Rome in 315 credits his victory, carefully, to "the inspiration of the divinity" without saying which one.

Was his conversion real?

This is one of the oldest debates in church history, and honest historians land in different places.

The sceptical view, made famous by the nineteenth-century historian Jacob Burckhardt, sees a calculating politician who used the Christian God as one more tool for power. Supporters point to his kept pagan titles, his solar coinage, and above all his actions: in 326 he had his own son Crispus executed, and his wife Fausta died soon after, almost certainly on his orders.

The sincere view, argued by historians such as Timothy Barnes and, from a theologian's angle, Peter Leithart, sees a man who genuinely believed the Christian God had given him victory and who grew in that faith. They point to his huge gifts to the church, his letters to bishops full of Christian language, his laws, and his attendance at Christian worship.

What about his deathbed baptism? Constantine was baptised only in 337, shortly before he died. To modern eyes that looks like insurance. In his own century it was common: many Christians delayed baptism because they believed it washed away all previous sin, and a man who had to order executions as part of his job had reason to wait.

The most balanced reading is probably that his faith was real but mixed — shaped by a Roman soldier's belief that a god gives victory, by political interest, and by genuine attachment to Christ. Only God sees the heart. What matters for our question is that his faith, sincere or not, did not create the faith he joined.

Nicaea, AD 325: what he did and did not do

In 318 or so, an Alexandrian priest named Arius began teaching that the Son of God was the first and greatest created being — exalted, but not eternal: "there was a time when he was not". The controversy split the churches of the east.

Constantine, now sole emperor after defeating Licinius in 324, wanted a united church in a united empire. He called a council of bishops at Nicaea, in modern Turkey, in 325. Somewhere between 250 and 318 bishops attended — the ancient sources differ — mostly from the eastern provinces. Some still bore the scars of persecution.

What Constantine did. He paid for the bishops' travel, opened the council, sat in on its sessions and pushed hard for agreement. According to Eusebius's letter to his own church, the emperor personally supported the key word homoousios — that the Son is "of the same being" as the Father. Afterwards he exiled Arius and the two bishops who refused to sign.

What Constantine did not do.

• He did not invent the deity of Christ. The bishops were not deciding whether Jesus was God as if it were a new question. They were rejecting a recent teaching that contradicted what Christians had confessed for generations — as John 1:1 and Philippians 2:5-11 already did. The vote was not close: only two bishops refused to sign.
• He did not choose the books of the Bible. No document from Nicaea discusses the canon. The Da Vinci Code claims Constantine commissioned a new Bible that left out older gospels portraying a human Jesus. There is no ancient evidence for this at all. What he did order, around 331, was fifty well-made copies of the Scriptures from Eusebius for the churches of Constantinople — the existing Scriptures, copied for new buildings.
• He did not enforce Nicaea consistently. Within a few years he had allowed Arius back, and in 335 he exiled Athanasius, the great defender of Nicaea. He was finally baptised by Eusebius of Nicomedia, a bishop sympathetic to Arius. His son Constantius II actively backed the Arian side. If Constantine had wanted to impose the deity of Christ by force, he went about it very strangely.

The Sunday law, AD 321

On 7 March 321 Constantine issued a law that begins: "On the venerable day of the Sun let the magistrates and people residing in cities rest, and let all workshops be closed." Farmers were allowed to keep working, so as not to lose good weather for planting.

This is the source of the claim that Constantine "changed the Sabbath". But Christians had been gathering on the first day of the week — the day of Jesus' resurrection — since the New Testament (Acts 20:7; Revelation 1:10). Around AD 150 Justin Martyr described the weekly gathering "on the day called Sunday", nearly two centuries before Constantine.

What the law did was give an existing Christian practice the backing of public law, in language a pagan population could also accept. That is a real change, and it shaped the rhythm of the week for centuries — including, in many African countries, the colonial-era Sunday that is still the main day of worship. But the day itself was older than the law.

What imperial favour gave the church

It would be ungrateful to tell this story only as a list of corrections. Constantine's reign changed the lives of millions of Christians for the better.

• Persecution ended. Believers who had watched friends burned and churches destroyed could worship openly. Confiscated property was returned.
• Churches were built. Constantine funded great basilicas in Rome, the Church of the Holy Sepulchre in Jerusalem, and the churches of his new capital, Constantinople. His mother Helena's journey to the Holy Land in the 320s began a long tradition of pilgrimage.
• Some laws became more humane. Historians generally credit him with abolishing crucifixion as a punishment, and he banned branding criminals on the face, reasoning that it disfigured the image of God. Churches gained the right to receive legacies, and clergy were released from costly civic duties so they could serve.

What it cost

The costs were real too, and Christians from many traditions have named them.

• The church gained power, and power attracted the wrong people. When being a Christian helped your career, some joined for the career. The desert monks of Egypt went into the wilderness partly in protest against a church grown comfortable.
• The emperor became a referee of doctrine. Constantine called councils and exiled bishops. Later emperors did the same, sometimes backing heresy rather than orthodoxy. The line between Christ's kingdom and Caesar's became blurred — "my kingdom is not of this world," Jesus had said (John 18:36).
• Christians began to use force against Christians. In North Africa, after the Donatist schism, Constantine sent troops against a dissenting Christian group around 317 — the first time a Christian emperor used the state's power against fellow believers. Sadly, it was not the last.

Here believers disagree. Some, especially in the Anabaptist tradition, see the whole partnership as a betrayal of the church's calling to be a distinct people. Others, including many Catholic, Orthodox and Reformed Christians, see it as a mixed but real providence — the gospel shaping laws and cultures for the better, despite the sin of the people involved. Romans 13 and Revelation 13 both describe the state; the church has always had to live between them.

The official religion? Not yet

One last correction. Constantine did not make Christianity the official religion of the Roman Empire.

After his death his sons quarrelled, the empire swung towards Arianism, and in 361 his nephew Julian — "the Apostate" — tried to restore paganism. It was only on 27 February 380 that the emperor Theodosius I, in the Edict of Thessalonica, declared that all his subjects should hold the faith of Nicaea. The following year the Council of Constantinople completed the Nicene Creed. In the 390s Theodosius went further and banned pagan sacrifice.

So the sequence is: legal toleration in 313, imperial favour under Constantine, and official state religion only in 380 — nearly seventy years after the Milvian Bridge.

Why it matters to you

If someone tells you Constantine invented Christianity, you can answer gently and with confidence. The faith, its Scriptures, its Sunday gathering and its worship of Jesus as God were all in place before he was born. What he changed was the church's place in the world.

That change is a lesson for any church that finds favour with the powerful — whether in fourth-century Rome or in a modern capital where politicians attend crusades and churches court their support. Favour can open doors for the gospel. It can also quietly change what the church is willing to say. Jesus' instruction still holds: "Render to Caesar the things that are Caesar's, and to God the things that are God's" (Matthew 22:21).