Early Christianity offered its adherents contact with the divine, community with fellow believers, and the promise of eternal life in heaven. But the religion was suspicious to the Romans for a number of reasons:

• It was not classy: it was a novelty (Romans respected antiquity in religion), and attractive to those on the lower end of the social pyramid, e.g. slaves, women, and merchants. Plus, they worshiped an executed criminal! As I like to say, it was like Scientology without the celebrities.

• Christians also met privately in people’s homes for their religious rituals. What were they up to? Romans practiced their religion in public, and the Twelve Tables forbade people meeting at night. If Christians had nothing to hide, then surely they wouldn’t be so secretive? It may have been a caricature of anti-Christian sentiment, but the notions of one Caecilius Natalis, a character in the Octavius of Minicius Felix (d. ca. 250), probably reflect a certain strain of opinion:

I hear that they adore the head of an ass, that basest of creatures, consecrated by I know not what silly persuasion, a worthy and appropriate religion for such manners. Some say that they worship the genitals of their pontiff and priest, and adore the nature, as it were, of their common parent. I know not whether these things are false; certainly suspicion is applicable to secret and nocturnal rites…

Now the story about the initiation of young novices is as much to be detested as it is well known. An infant covered over with meal, that it may deceive the unwary, is placed before him who is to be stained with their rites: this infant is slain by the young pupil, who has been urged on as if to harmless blows on the surface of the meal, with dark and secret wounds. Thirstily – O horror! they lick up its blood; eagerly they divide its limbs. By this victim they are pledged together; with this consciousness of wickedness they are covenanted to mutual silence.

You can see how the liturgical consumption of bread and wine, designated the “body” and “blood” of Jesus, might lead to this accusation of ritual murder and cannibalism. (Ironically, Christians would accuse Jews of doing much the same thing during the Middle Ages.)

• Perhaps most important, the religion was monotheistic. Or rather – Christians claimed to be monotheists, and spent a good deal of mental energy attempting to save this particular appearance, even though their God had three different aspects in a complex relationship. But they were not tolerant of any other gods, and unlike the Romans, who were religiously broad-minded and instinctively syncretic, Christians refused to acknowledge even the possibility that other deities existed. The Romans, for their part, could not understand this. They didn’t care what you actually believed; participating in the state sacrifices was like standing for the national anthem. Just do it! Then go and do whatever else you want. But when Jupiter looks down and sees that not all the people in the city are honoring him, he might get cranky and punish it. So Christianity was sporadically persecuted by the Roman authorities, not because of anything that the Christians believed, but because of their refusal to participate in the state sacrifices. They represented a security risk.

But in one of the most remarkable reversals in history, Emperor Constantine (306-337) called it all off (his predecessor in office, Emperor Diocletian, was a particularly enthusiastic persecutor of Christians). Constantine’s mother was a Christian, and the Battle of Milvian Bridge (312) sealed the deal: he claimed that God gave him the victory, so he became the patron and protector of Christianity over the course of his long reign. Not only that, but he established a Christian dynasty; following Constantine, all emperors were Christian (except for Julian the Apostate, who reigned for only two years in the 360s). Thus, over the course of the fourth century, the Roman Empire was increasingly Christianized, and its traditional paganism increasingly denigrated. The two classic documents to illustrate this trend are Edict of Toleration of 313, which granted protection to Christians and restored their expropriated property, and the Theodosian Code of 380, which essentially outlawed paganism.

Needless to say, this shift profoundly changed the Roman Empire. But it also changed Christianity – for good and for ill. If nothing else, Christians had to go from hating the empire to defending it, which was psychologically discombobulating. They had to imagine that the conversion of the empire was all part of God’s plan all along. Now it is safe to say that this phenomenon is why Christianity exists today. If the conversion had not occurred, Christianity may very well have gone the way of Mithraism or the cult of Isis. So some people see the conversion of the Empire as a profound triumph. Others see it as an example of someone gaining the world but losing his own soul. In the third century, there were certain benefits to being a Christian, but you stood a very real chance of dying for your faith if you became one. So you had to mean it. Now that Christianity had the backing of the state, people started to convert opportunistically, and so it lost some of its fervor. You didn’t need to be a Christian to get a job with Constantine, but it sure helped. So people became Christians, but did they really mean it? At the same time, Constantine may have been Christian, but he was still the emperor, meaning that he had to do all the political things that emperors do, like executing criminals, waging war, cheating people to reward others, etc. Like a political party out of power, at one point Christians could afford to be ideologically pure, but once they got their hands on power, they needed to make all sorts of compromises. (Right from the start! Does the God of the Christians really make his will known by the results of battles?)

Some other effects of the conversion of the fourth century include:

• A concern with orthodoxy (“correct belief”). The longer that Christianity went on, and the wider it spread, the more likely it was that different people would adopt different opinions about what it all meant. When the state was persecuting Christians, these differences were of secondary importance, but once the state started to favor Christians, they immediately started sniping at each other and jockeying for position. Constantine, embarrassed by this, personally called the Council of Nicaea (325) to sort out the question of whether “there was a time when Jesus was not.” (Answer: No! Don’t be fooled by the titles “God the Father” and “God the Son” – the one did not give rise to the other, as the names would suggest; both of them, along with the Holy Spirit, existed from before all time.) Since Christianity is not tied to a particular ethnic group, there is nothing to distinguish the Christian from the non-Christian except belief, expressed through the Creed (from credo, “I believe”). Christianity acted like Communism, with a party line that you had to adhere to. If you didn’t, you were a heretic (from the Greek word for “choice,” which was invariably a wrong choice). The early Christians did not “celebrate diversity” the way we do – “following the devices and desires of our own hearts” will lead straight to Hell, and people need firm guidance to in order avoid it. Other opinions declared heretical around this time included Pelagianism (the idea that you can work your own salvation), Donatism (the idea that the sinfulness of a priest renders the communion he performs inoperative), and Monophysitism (the idea that Jesus had only one divine nature while on earth, instead of two).

• A concern with theology. When educated pagans converted to Christianity, they were appalled at its intellectual poverty. Thus did St. Augustine (354-430) and other so-called Doctors of the Church attempt to provide some philosophical heft to the religion. Augustine’s City of God, for instance, provided a Christian interpretation of all world history. In one of his letters to the Corinthians, St. Paul had declared that the world’s wisdom was foolishness. After the fourth century, this was no longer the case.

• A reimagining of the concept of sainthood. At the very start, I understand, Christians called each other “saint” (“holy”) in the same way that Communists used to call each other “comrade.” Members of the LDS church still adhere to this custom. Soon the title was reserved for martyrs: people who had been witnesses for their faith, even unto death. Martyrdom was a one-way ticket to heaven and martyrs were hugely prestigious for the Christian communities that produced them. Tertullian said that “the blood of the martyrs is the seed of the church”; a more contemporary way of putting this would be “You can’t win, Darth. If you strike me down, I shall become more powerful than you can possibly imagine.” But with the conversion of the empire, there were no more martyrs being created. Some people felt relieved about this, I’m sure. Others were deeply disappointed, as though they were always hoping to achieve this happy state. The disappearance of martyrdom did not lead to a withering of the concept of sainthood, however: other servants of the church like competent and well-loved bishops, generous church patrons, or learned theologians could all became saints, and did.

• The advent of the intercessory power of sainthood. With the conversion of the empire, it was easy to figure heaven as parallel to the imperial court. Just as a supplicant could not approach the emperor directly, but had to go through one of his courtiers, so also Christians started to think that it was presumptuous to pray directly to God. It was much better to go through a saint, who was in heaven with God and who had his attention, but who had once been human and was familiar with human concerns. The saint could pass your prayer on to God; he might even be deputized to answer prayer himself. Thus did certain saints come to exercise particular competencies, which were often suggested by details from their lives: if St. Lawrence was executed on a gridiron, he could become the patron saint of cooks; if St. Lucy had her eyes gouged out, you should pray to her if you’re experiencing eye trouble.

• An emphasis on relics and pilgrimage. Some people claim that the Christian veneration of relics (the bones of saints, and other things they left behind) grew out of the pagan cult of heroes. Indeed, there is an interesting story in book one of the Histories of Herodotus, when the Spartans asked the Oracle at Delphi whether they should go to war again against Tegea, and the Oracle replied they should acquire the bones of Orestes, son of Agamemnon – which they did, and which helps to explain the Spartan advantage in war. But the pagans were nowhere near as obsessed with relics as Christians were, and to my mind the Christian interest in relics derives from their doctrine of the resurrection of the dead – in the Last Days, the dead will be raised for the final judgment. Saints retained a certain connection with their earthy remains, which Christians treated with the utmost respect. (All the same, I suppose the notion of relics holding power would be something that a newly-converted pagan would understand.) Prayers to saints were particularly effective in the presence of these relics, so people would sometimes travel long distances to make their requests (or to give thanks for prayers already answered). This is known as pilgrimage and it was a distinctive feature of medieval Christianity.

• The rise of monasticism. If martyrdom was no longer an option, some people tried to become ascetic “living martyrs.” The entire empire was ostensibly Christian, but it was just as bad as it ever was, so some people wanted to withdraw from it. St. Anthony (d. ca. 356) was one such – he withdrew into the Egyptian desert, ate as little as possible, and prayed full time to God. (Unfortunately for him, he achieved such a reputation for holiness that he attracted great throngs of people seeking his advice.) His performance was designated “eremitical” monasticism, and it inspired numerous other people hoping to reach the same level of holiness. Not everyone was quite as dedicated as Anthony, however, and eventually some of these desert fathers began pooling their efforts – one person went to look for food, while the others stayed behind to pray or do other tasks. This represents the beginning of “cenobitical” monasticism, which achieved its most celebrated form in The Rule, a blueprint for establishing a community of monks, by St. Benedict of Nursia (480-547). Monks, especially Benedictine monks, became a regular feature of life throughout the medieval west.

Needless to say intercessory sainthood, relics, pilgrimage, and monasticism are not endorsed by the Bible and as a consequence were rejected by most Protestants in the sixteenth century. A lot of them were skeptical of the conversion of the empire.