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Constantine's Conversion to Christianity: Was It Real? Does It Matter?

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One of the major turning points in the history of the church was Constantine’s conversion to Christianity.

Some Christians consider Constantine a saint. Others treat him as a politician, who only used Christianity for political purposes. And still others believe Constantine’s conversion was sincere—but that he also used Christianity for his own gain.

Let’s take a deeper look at Constantine’s conversion—both the motives behind it and the effect it had on the church.

Who was Constantine?

Constantine was the first Christian emperor. His reign began in 306, and after a series of internal struggles, he consolidated his rule over the entire Roman Empire in 324. In addition to his successful military campaigns, Constantine made several administrative changes that established and extended his influence.

In the history of Christianity, Constantine is most remembered for bringing state-sanctioned persecution to an end.

What do the sources say about Constantine’s conversion?

Constantine had two visions. The first, according to pagan sources, was a vision of Apollo in the year 306. In this vision, he was given 30 wreaths, symbolizing the 30 years he would reign as emperor.

But according to Christian sources, the vision that mattered wasn’t in 306, but in 312. And it wasn’t at the temple of Apollo, it was at the battle of Milvian Bridge.

Eusebius describes the event:

A most marvelous sign appeared to [Constantine] from heaven, the account of which it might have been hard to believe had it been related by any other person. . . . He said that about noon, when the day was already beginning to decline, he saw with his own eyes the trophy of a cross of light in the heavens, above the sun, and bearing the inscription, CONQUER BY THIS. At this sight he himself was struck with amazement, and his whole army also, which followed him on this expedition, and witnessed the miracle.

Was the whole incident fabricated? Was it a figment of his imagination? And, if he dreamed something or saw something, what was it?

A likely explanation is that he did indeed have some kind of experience—a dream, a vision, or both—but that the interpretation was provided by Christian advisers (notably Ossius, or Hosius, bishop of Cordoba, Spain). They may have helped Constantine to see in his experience the monogram of Christ as the Christian interpretation of what he saw.

After the vision, Constantine instructed his soldiers to put the Chi Rho monogram of Christ on their shields. This Christogram became an almost ubiquitous Christian symbol, often combined with the letters alpha and omega (the first and last letters of the Greek alphabet), for Christ as the beginning and the end.


Constantine’s smaller army won the battle of Milvian Bridge, and he secured control of Rome. Eusebius interpreted the event in grand biblical terms, comparing the defeat of Maxentius’s army to the destruction of the Egyptians under Pharaoh in the Red Sea.

When did the empire favor Christianity?

After this, Constantine began to favor Christians, and he slowly began to shift the ideological underpinnings of the Roman Empire.

The most important event in this shift happened the next year, in 313, when Constantine entered into an agreement with Licinius at Milan. This agreement, the “Edict of Milan,” granted the free exercise of religion to “Christians and all others.”

The second significant change happened in 330, when Constantine left Rome. He had become uncomfortable with the pagan associations of the city. Instead, he began to favor the wealth, commerce, and culture of the eastern empire.

He founded a new capital on the site of the old Greek city of Byzantium and named it Constantinople. Today it’s the modern city of Istanbul.

His rule in Constantinople laid the basis for the orthodox Christian empire known as the Byzantine Empire, which would last more than 1,100 years.

Strangely, Constantine wasn’t baptized until near his death. This set a precedent for others in the fourth century who delayed their baptism until their old age or their death bed so as to obtain the maximum benefit of the forgiveness of sins.

How did the church respond to Constantine?

Throughout his lifetime, Constantine favored Christians and the role of Christianity in the empire.

He gave bishops the privilege of adjudicating disputes, and their decisions had the same status as decisions by civil judges.

He also initiated an extensive church building program. He built the Church of the Nativity in Bethlehem; the Church of the Holy Sepulcher in Jerusalem; churches to commemorate the martyrdom of Peter and Paul; the Lateran basilica; and many others.

At the same time, although he was permissive of Christian practice in the empire, he was also lenient toward pagan religious practices. Many of his actions were designed not to offend pagans or were subject to ambiguous interpretation. For example, the prayer he composed to be recited by the army was religiously neutral between pagan and Christian monotheism. And the legislation making Sunday a legal holiday gave leisure to Christians for their church assemblies, but was worded as an honor to the sun.

With Constantine’s conversion, the church found itself in a new position: the emperor became the most powerful proponent of Christianity. This caused three major problems:

1. The competence of the state in church affairs

Church-state relations changed radically in the years after Constantine’s conversion. The church was simply not prepared for the change from a persecuted church to a favored church.

Some people, like Eusebius, saw the empire’s recognition of Christianity as an act of God’s providence. Others took a more sober line, and stressed the responsibilities now placed upon the authorities charged with Rome’s welfare.

2. The nature of the church itself

The Donatist schism raised anew the question of the holiness of the church: Is the church the church of the pure, or is it a mixed body, a “hospital for sick souls”? Can a church of the majority and of a ruling class be a holy church?

The changed circumstances also prompted the rise of monasticism. Monks sought to work out the true Christian life with the same intensity that had characterized the times of persecution. Denied literal martyrdom, they attempted a martyrdom of self-denial.

3. The definition of doctrine

The definition of doctrinal orthodoxy was brought to the forefront by the Trinitarian controversy, sparked by the teachings of Arius. Doctrinal controversy threatened the unity of the church and with it Constantine’s goal of harmony in the empire. The problems of Arianism and Donatism both arose during Constantine’s reign. They raised fundamental questions about the definition of the church and of the deity it worshiped.

The definition of doctrinal orthodoxy was brought to the forefront by the Trinitarian controversy, sparked by the teachings of Arius. Doctrinal controversy threatened the unity of the church and with it Constantine’s goal of harmony in the empire. The problems of Arianism and Donatism both arose during Constantine’s reign. They raised fundamental questions about the definition of the church; Constantine called the Council of Nicaea to help resolve these questions.

How do most Christians view Constantine today?

Sometimes one’s faith and convictions prove to be the politically expedient course of action. Since it can often be difficult to know our own motives for the actions we take—and even more difficult to understand the motives others take for their actions—we need to be careful about jumping to conclusions about Constantine’s conversion.

Whatever the case, one thing is certain: Constantine and his successors created a civil society composed mostly of Christians, and in which Christianity was the dominant force. It prompted the church to respond to new challenges—both doctrinal and cultural.

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There is much more to learn about Constantine. As a next step, sign up for a brand new online course taught by Everett Ferguson, Church History 1.

In this course, you will discover:

  1. Who the most important figures in church history are
  2. What the key controversies in the church were, and how they still shape the church today
  3. Which ideas defined and shaped the church during its first 1,200 years
  4. The significant turning points in church history, including the Roman emperor Constantine’s conversion to Christianity, the Great Schism between churches of the East and West, the Crusades, and numerous others
  5. The dynamic relationship between broader world history and church history

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Or, to learn how you can offer this online course at your church or school, contact us today!

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