Church History · AD 380

Christianity Becomes the Official Religion of Rome

On February 27, 380, Emperor Theodosius I issued the Edict of Thessalonica, making Nicene Christianity the official faith of the Roman Empire. Church and state were joined together, which brought both real blessings and real harm.

Read it in the Bible: Mark 12:17 John 18:36 Romans 13:1-7 Hebrews 12:28

Christianity became the official religion of the Roman Empire on February 27, AD 380, when Emperor Theodosius I issued the Edict of Thessalonica. It ordered all the peoples of the empire to follow the faith taught by the apostle Peter and held by the bishops of Rome and Alexandria, meaning the Trinity as confessed at Nicaea. Less than 80 years earlier, Diocletian had been burning Bibles. Now the emperor was telling everyone to be a Christian. That change shaped the church, for good and for bad, for more than a thousand years.

Who Was Theodosius I?

Theodosius was a Spanish born general who became emperor of the East in 379, after the Goths crushed a Roman army at Adrianople. He was a committed Nicene Christian, which means he believed Jesus is fully God, as the Council of Nicaea had taught in 325. At the time, many church leaders in the East, especially in Constantinople, still followed Arian teaching, which said the Son was created.

Around this time he fell seriously ill in Thessalonica and was baptized. He then moved to settle the matter by law. He was the last emperor to rule both halves of the empire, and when he died in 395, it split for good into East and West.

What Did the Edict of Thessalonica Say?

The edict was issued in the names of Theodosius and the two western emperors, Gratian and Valentinian II. It is often called by its first Latin words, Cunctos populos, meaning all peoples. It said that everyone in the empire should hold the religion that the apostle Peter had delivered to the Romans. It named Damasus, bishop of Rome, and Peter, bishop of Alexandria, as examples of that faith. It defined that faith as belief in one God, Father, Son and Holy Spirit, equal in majesty.

Those who accepted it were to be called Catholic Christians. Everyone else was labeled a heretic. The edict calls them foolish madmen, says their meetings may not be called churches, and warns that they will face God's judgment and then the emperor's punishment. It was later included in the Theodosian Code, the official book of Roman law.

Wasn't Christianity Already Official Under Constantine?

No, and this is a very common mixup. Constantine's Edict of Milan in 313 made Christianity legal, and he gave the church a lot of support. But paganism stayed legal, and the emperor still held the old pagan title of chief priest. The Constantine page on this site covers that story.

Theodosius went further. After 380, he and his successors passed more laws. In 381 he called the Council of Constantinople, which confirmed and expanded the Nicene Creed. In 391 and 392 he banned pagan sacrifices and closed temples. The Olympic Games, tied to the worship of Zeus, ended around this time too. Within a generation, being a pagan in the Roman Empire went from normal to illegal.

What Good Came From Christianity Becoming Official?

A lot of good came from it.

Persecution of Christians was over for good inside the empire.
The church could build openly, train leaders and copy Scriptures on a large scale.
Christian care for the poor, the sick and widows grew. Bishops like Basil of Caesarea built some of the first hospitals.
Christian ideas about the worth of every person, including slaves, women and children, began to shape law and culture.
The church held rulers to account. In 390, after Theodosius ordered a massacre in Thessalonica, Bishop Ambrose of Milan refused him communion until he publicly repented. An emperor kneeling in repentance was something the ancient world had never seen.

What Harm Came From Joining Church and State?

The same power that protected the church also tempted it.

People joined the church because it was good for their careers, not because they believed. Many churches filled with people who were Christian in name only.
Force was used against pagans, Jews and Christians who disagreed. Temples were sometimes destroyed by mobs. In 385 a Spanish bishop named Priscillian was executed for heresy, one of the first Christians put to death by other Christians. Many church leaders, including Ambrose and Martin of Tours, protested.
Bishops gained political power and wealth, and church offices could become prizes to fight over.
The idea that the government should punish wrong belief led, over the centuries, to darker chapters like the Inquisition and the burning of reformers such as Jan Hus.

Many Christians in the Anabaptist, Baptist and free church traditions see 380 as the start of a long wrong turn. Many Catholic and Orthodox Christians see it as the natural result of an empire coming to faith, while also regretting the abuses. Both sides agree on this much: faith that is forced is not faith at all.

What Did Jesus Say About Church and State?

Jesus did not set up a political kingdom. When asked about paying taxes to Rome, He drew a line between the two.

Then Jesus told them, “Give to Caesar what is Caesar’s, and to God what is God’s.” And they marveled at Him. Mark 12:17

Paul taught Christians to respect governing authorities, and also that the church's weapons are spiritual. The early church grew under persecution by love, truth and courage, not by law.

Why the Year 380 Matters for You Today

Every Christian still faces the question Theodosius faced: how should faith and power relate? It is tempting to want the government to make everyone act like Christians. But history shows that when the church reaches for the sword, it often cuts itself.

Jesus' kingdom spreads one heart at a time, by the Spirit and the word. Governments rise and fall. Rome itself fell in the West less than a century later. His kingdom does not.

Therefore, since we are receiving an unshakable kingdom, let us be filled with gratitude, and so worship God acceptably with reverence and awe. Hebrews 12:28

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Questions People Ask

When did Christianity become the official religion of Rome?

On February 27, AD 380, when Emperor Theodosius I, with Gratian and Valentinian II, issued the Edict of Thessalonica. It made Nicene Christianity, belief in the Trinity, the official faith of the empire. Laws in 391 and 392 then banned pagan sacrifice.

Did Constantine make Christianity the state religion?

No. Constantine legalized Christianity with the Edict of Milan in 313 and strongly supported the church. But paganism remained legal during his reign. Christianity became the official religion under Theodosius in 380.

What was the Edict of Thessalonica?

It was a decree, also known by its Latin opening Cunctos populos, ordering all people in the empire to follow the faith taught by Peter and held by the bishops of Rome and Alexandria. Those who did were called Catholic Christians, and others were labeled heretics. It is preserved in the Theodosian Code.

Was it good for the church to become the state religion?

Christians disagree. It ended persecution and helped the church care for the poor and spread the faith. But it also brought nominal faith, political power struggles and, over time, the use of force against those who believed differently.

Sources

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