Constantine was the first Christian emperor.  In my book The Triumph of Christianity (Simon & Schuster, 2018), I devote two chapters to how, when, and why he converted (and if he did!), and to what difference it made to the world.  Here is a taste of it for those of you interested in checking out the book.  And for those of you who are not.

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Few events in the history of civilization have proved more transformative than the conversion of the emperor Constantine to Christianity in the year 312 CE.  Later historians would sometimes question whether the conversion was genuine.  But to Constantine himself and to spiritual advisors close to him, there appears to have been no doubt.  He had shifted from one set of religious beliefs and practices to another.  At one point in his life he was a polytheist who worshiped a variety of pagan gods — gods of his hometown Naissus in the Balkans, gods of his family, gods connected with the armies he served, and the gods of Rome itself.  At another point he was a monotheist, worshiping the Christian God alone.  His change may not have been sudden and immediate.  It may have involved a longer set of transitions than he later remembered, or at least said.  There may have been numerous conversations, debates with others, and reflections within himself.  But he dated the event to October 28, 312.  At that point he began to consider himself a Christian.

The results were tremendous, but not for the reasons often claimed.  It is not that Constantine eventually made Christianity the state religion.  Christianity would not become the official religion of Rome until nearly eight decades later under the reign of emperor Theodosius I.  And it is not that Constantine’s conversion was the single decisive turning point in the spread and success of the Christian religion, the one moment that changed all history and made the Christian conquest a success.  At the rate it was growing at the time, Christianity may well have succeeded otherwise.  If Constantine had not converted, possibly a later emperor would have done so, say, one of his sons.   Instead, what made Constantine’s conversion revolutionary was that the imperial apparatus that before then had been officially opposed to Christianity and worked hard, in some regions of the empire, to extirpate it completely, suddenly came to support it, promoting Christianity instead of persecuting it.  Constantine did not make Christianity the one official and viable religion.  He made it a licit religion, and one that enjoyed particular, even unique, imperial privileges and funding.  This support did indeed advance the Christian cause.  The recognition that this faith was now favored from on high appears to have contributed to the already impressive numbers adding to the Christian growth, including the conversion of increasing numbers of imperial and local elites, whose resources had until then funded (and thus made possible) the religious practices of their pagan world.

As important as Constantine’s conversion was to the welfare of the Christian movement, it is surprisingly difficult to describe what he converted from.  Modern historians of religion who speak of conversion can mean a variety of things by it.  Possibly it is simplest to keep the meaning broad and use the term to refer to a decided shift away from one set of religious practices and beliefs to another.   That certainly happened with Constantine.  At a moment that seemed, at least later in hindsight, to be clear and well-defined, he stopped being a pagan and became a Christian.

Conversion was not a widely known phenomenon in antiquity.  Pagan religions had almost nothing like it.  They were polytheistic, and anyone who decided, as a pagan, to worship a new or different god was never required to relinquish any former gods or their previous patterns of worship.  Pagan religions were additive, not restrictive.

Christians, on the other hand, did require a choice.  Converts were expected to forego the worship of all the other gods and revere the Christian God alone.   Only Judaism had similar expectations and demands.  Among pagans – that is among the 93% or so of the world that by custom, habit, and inclination worshiped multiple gods – worshiping a range of divine beings was not a religion that anyone chose.  It was simply what people did.  Being a pagan meant participating in the various religious activities associated with the official state gods, local municipal gods, personal family gods, and any other gods that were known to be involved with human experience.  For everyone except Jews, and then Christians, this was more a way of life than a conscious decision.  It  was a matter of doing what everyone had always done, very much like participating in the life of the local community, with the exception that most people were involved with only one community but could be engaged in the worship of a virtually incalculable number of gods.

For that reason, paganism should not be thought of as a solitary “thing” but as hundreds – thousands – of things.  Those who practiced traditional religions – in other words, just about everyone – would never have recognized themselves as participating in something called “paganism” or, indeed, any kind of “ism.”   There was not a thing there, nothing that could be named so as to sum up the totality of all the non-Jewish religious observances or beliefs or cultic practices of prayer and sacrifice ubiquitous in the culture.  No pagan would have understood what it would mean to call themselves pagan.  They were simply acting in time-honored ways of worshiping the gods.

Constantine, like everyone else who was not raised Jewish or Christian, participated in this worship.  But he gave it up to follow the one God of the Christians.  The narrative of how Constantine became a Christian is both intriguing and complex.  It involves issues that we today would consider strictly social and political and other issues that we would consider strictly religious.  But in the early fourth century – as in all the centuries of human history before that time – these two realms, the socio-political and the religious, were not seen as distinct.  They were tightly and inextricably interwoven.  On just the linguistic level, there were no Greek or Latin terms that neatly differentiated between what we today mean by “politics” and “religion.”   On the practical level, the gods were understood to be closely connected with every aspect of the social and political life of a community, from the election of officials, to the setting of the annual calendar, to the laws and practices that governed social relations, such as marriage and divorce, to the administration of civil justice, to the decisions and actions of war, to all the other major decisions of state.    The gods were active in every part of social and political life, and the decisions made and actions taken were done in relation to them.

On the imperial level this meant that it was widely known (and genuinely believed, by most) that it was the gods who had made the empire great.  The empire responded by sponsoring and encouraging the worship of the gods.  Doing so would promote the commonweal.  There was no sense that there was, should be, or could be a separation of church and state.

Starting in the mid-third century, the emperors themselves sensed this full well and acted accordingly.  That is why, some years before Constantine converted, the Christian religion had been persecuted by order of the state.  The Christians refused to worship or even acknowledge the gods of empire, claiming in fact that these were evil demonic beings, not beneficent deities that promoted the just cause of the greatest empire the world had ever known.  The refusal to worship was seen by others to be dangerous to the well-being of empire and thus to the security of state.  And so the decision to persecute – which seems to us, perhaps, to be a strictly religious affair – was at the time inherently socio-political as well.  The Christians were to be removed like a cancer from the body of state.  No emperor came to believe this more firmly – in no small part because of the alarming growth of this cancer – than Constantine’s predecessor on the throne, Diocletian, who instigated the most vicious empire-wide persecution ever seen.  Constantine himself was later to rescind the demands of this persecution.  But while it was still in process, he converted.

This conversion proved to be a lynchpin of imperial history, not just for the fate of the Christian religion but also for the workings of the Roman state.  We will look at the persecution of Diocletian in a later chapter, and at the broader biography of Constantine in another.  For now we are interested specifically in his conversion and how it radically changed the balance of power, both for the persecuted Christians and for the running of the Roman government.  To make sense of the conversion we need to understand some of the political and religious backdrop to the story.