In This Sign: The Legacy of Constantine for Church and World

                                                                                    Emperor Constantine 

Introduction

Kerk & Leven (“Church & Life”) is the leading weekly Catholic magazine in the Flemish region of Belgium. Since October 2025, on the invitation of the chief editor of the local edition of the parish of Olen, Cis Marinus, I have been writing a reflective article every two weeks from a philosophical and theological perspective, exploring Christianity in a scientific age.

11 March 2026

In This Sign: The Legacy of Constantine for Church and World

In the first centuries after Jesus of Nazareth, we cannot yet speak of Christianity as a true, distinct, new religion. It is only through the Roman emperor Constantine (280–337) that, in the fourth century, Christianity gradually takes on the form as we know it today.

Let me take you back in time for a moment, to the year 234 AD, when the 14-year-old emperor Severus Alexander, unable to cope with his task, is murdered by the army. A period of total political chaos breaks out and lasts for decades. When Emperor Diocletian is forced in 305 to leave Rome and flee to Split in present-day Croatia, a new form of government emerges: the ‘diarchy’, a rule by two people. This soon becomes four: two emperors and two vice-emperors, the ‘tetrarchy’. They divide the Roman Empire into four parts among themselves. The Roman Empire is on the verge of falling apart.

Constantine is born in 280 in Britannia (present-day England), the son of Constantius, one of the four tetrarchs. When his father dies in 306, Constantine decisively takes control. However, he wants to abolish the tetrarchy and marches on Rome. His rival, General Maxentius, is lured into a battle just outside the city, at the Milvian Bridge.

In 312, Constantine wins the battle against Maxentius and becomes sole ruler of the Roman Empire. According to legend, on the evening before the decisive battle he has a vision: in the clouds he sees a cross and hears the words “In hoc signo vinces” (“In this sign you will conquer”). Constantine resolves to convert to Christianity if he wins the battle. And so it happens, although Constantine is only baptized on his deathbed in 337.

Although Constantine himself knows very little about Christianity, he sees in it a great potential for a moral “revival” in response to the severe crisis still raging in the Roman Empire. He wants to use Christianity as a kind of moral binding force to counter the threat of further disintegration of the empire.

As a first step, Emperor Constantine issues the Edict of Milan in 313. This edict guarantees, among other things, freedom of religion for all Christians. As a result, Christians are no longer persecuted. In 318 follows the Audientia Episcopalis (“arbitration by the bishop”), a true turning point in history. Through this law, Christianity receives several important privileges. Bishops are officially installed as judges, giving them the legal authority to settle disputes. This makes the office of bishop a highly attractive and sought-after position.

But then a serious problem emerges: Christianity itself, on which Constantine had placed so much hope as a political remedy, shows deep fissures. Constantine decides to intervene. This looming rift in early Christianity has everything to do with a certain Arius, who claims that Jesus is not fully divine, but created by God. Some bishops strongly condemn this idea, while others firmly support it. The result is great unrest and the threat of an actual schism.

Constantine wants to put a stop to this and convenes the Council of Nicaea in 325, with himself presiding, to force a solution to this thorny issue. At Constantine’s request, the Nicene Creed is formulated here, which is still recited during the Eucharistic celebration today. In this creed, Jesus is said to be “of the same substance” as the Father (in the official English translation: “consubstantial with the Father”). Jesus is said to be “ὁμοούσιον τῷ Πατρί” (homo-ousion tooi Patri), “of the same substance as the Father” (Latin: consubstantialem Patri), thus fully God, not created by God. As a consequence, Arianism is condemned as heresy. In short: the divinity of Jesus is established by Roman law in 325 at the Council of Nicaea under Emperor Constantine, or more precisely, the divine equality of God the Father and Jesus the Son. This clever strategy will be repeated several times: in 381 (First Council of Constantinople), the divine equality of the Holy Spirit is established by Roman law, and in 451 (Council of Chalcedon), the doctrine of the Holy Trinity is established in the same manner.

At this same Council of Nicaea, the first foundations of canon law also emerge. Constantine seeks “orthodoxy” (believing the same things): for him, it is crucial that doctrines of faith are precisely defined and not open to question. He needs this orthodoxy to use Christianity as a unifying force for the disintegrating Roman Empire. This leads Christianity to take on a unique position among the major world religions: in other religions, the focus is on “orthopraxy” (doing the same things), while what one believes is often left more open.

Moreover, alongside orthodoxy, Constantine also wants sufficient control: to achieve this, he needs Christians in public buildings. Until then, there are only “house churches”: Christians have gathered in homes for centuries. Instead of using existing temples in the city center, Constantine chooses a specific type of building outside the city center: the basilica. On the site of the barracks of his former enemy Maxentius, he builds the Lateran Basilica. This too proves to be a masterstroke. The Roman basilica is the architectural form used for courts of law. Constantine’s intention in choosing this type of building is that a court conveys authority and power, qualities that are then translated into church buildings.

When the Western Roman Empire falls in 476, the territory is divided, with Gaul (present-day France) going to the Franks. The Franks, however, are not Christians. Once again, historical circumstances create a turning point. Had history unfolded slightly differently, Christianity might have disappeared from Western Europe with the fall of the Western Roman Empire. Crucial for its survival is the figure of Clovis I, king of the Franks, who converts to Christianity at the end of the 5th century. This conversion has nothing to do with piety and everything with strategic calculation. After the fall of the Western Roman Empire, most Romans in Gaul continue living as they always had. Many of them are already Christians. By converting, Clovis hopes to win the favor of the population. This marks the definitive beginning of Christianity as we know it today.

Constantine’s legacy has been decisive for both the Church and the world. Over the centuries, Christianity would grow into the largest of the world religions, a striking example of how contingent historical events can profoundly shape world history.