The Spread of Christianity

We haven’t really talked about how this group became the world’s largest religion, and the rise of Christianity is something I remember from being a Christian that myself and others would fall back on. In response to arguments like the ones we’ve talked about the last few episodes, Christians always have this safety net. Wasn’t Christianity’s growth rate and it’s current size at least evidence in support of it? Before we talk about the material, historical causes behind the rise of Christianity, we should examine whether this reasoning is valid to begin with.

Christians claim that the rise of Christianity was so unusual to suggest it was divine. And of course, it was unusual. A small, forbidden cult spread across the West, despite early persecution, and went on to become the world’s largest religion. We shouldn’t undersell the spread of Christianity. This is as strange as a cult with two dozen people gaining millions of followers in a few centuries. The situation we’re currently living in would be just as strange as traveling a few hundred years into the future and discovering that the Branch Dividians had hundreds of millions of followers.

Logically, the idea that the number of people who hold a belief matters at all when determining whether or not that belief is true is obviously wrong. And of course, every religion with a significant following once started as a small group and had a meteoric rise from a few to millions. No religion began with a hundred million followers. Once you acknowledge that there are in fact millions of Muslims, Jews, Mormons, Hindus, and so on, you have to recognize, no matter which religion you belong to, that it must be possible for a religion that began with a handful of followers to gain hundreds of millions — or in some cases, billions — without being true. No matter which religion you belong to, you have to concede that numbers in and of themselves can’t be evidence of truth.

What about all the places that have never even heard of Christianity and haven’t had the chance to accept or reject it? Why has this progression been so inefficient if it’s guided by divine power? Christianity is not even close to being the majority, and especially not when you consider that the roughly 30% we’re calling “Christianity” is not a cohesive 30%. I don’t see any conflict between naturalism and the fact that all the different versions of Christianity combine to make up less than one third of the world’s religions. I don’t even think that fact is more likely on Christianity than on naturalism. If there was an omnipotent god trying to spread Christianity, wouldn’t you expect them to be a little more successful and a little more on the same page? Christianity is not one thing; to an outsider, they all look like they’re loosely based on the same mythology, but their actual beliefs matter. There are many incompatible branches and subgroups within that roughly 30%, so it doesn’t really make sense to speak of ‘Christianity’. The Mormons and the Russian Orthodox can’t both be right, and neither can the Lutherans and the Anabaptists. Many distinct faiths that fall under the umbrella of Christianity in that one-third figure are mutually exclusive. If God were invested in this particular religion, you’d think he would want to make it clear what he wanted. He could ensure that false branches of Christianity, or entire false religions wouldn’t spring up, and he would have every interest in doing so. Is he unable to prevent false religions from arising and deceiving us, or is he unwilling, for whatever reason?

If you’re a Catholic who believes most Protestants, Mormons, and Eastern Orthodox are not going to make the cut, the number is way less than one third. Whatever denomination of Christianity you happen to belong to — if you think that your specific branch is the only way, then you have to reduce the already modest, not-quite 33% to whatever your particular broad denomination is, and then you have to cut out all the believers in your own branch who you believe to be insincere or differ in nontrivial ways. At the end of the day, no matter which version of Christianity you adhere to, you should expect to get the wrong answer just as a matter of probability. The majority is going to be wrong, and the odds are always that you’re in the majority. If every non-Christian is wrong, and every version of Christianity except yours is wrong — then no matter what your belief is, 90% of the human population, conservatively, doesn’t believe the truth and is hopelessly doomed. Wasn’t the original point of this apologetic to try to appeal to the stunning takeover of the one true religion? If 95% of everyone is wrong, according to you, you shouldn’t really be bringing up your religion’s rate of success.

All these facts fit better in a naturalistic model than a Christian model of the world. The most reasonable form of this argument from apologists is that the success of Christianity is more likely on Christianity than on naturalism. But I’m saying that even that evidential form of the argument doesn’t hold water. Yes, you certainly would expect god’s favored religion to be the most popular. But the one third of people who are “Christian” don’t agree on important parts of the story. When you break down the category of ‘Christian’ into it’s irreconcilable denominations, you don’t end up with a third, or a fourth, or a tenth of the human population. You end up with dozens and dozens of mutually exclusive religions that center loosely around similar themes. This makes sense on naturalism — you wouldn’t expect uniformity on naturalism, like you would on theism. You’d expect religions to evolve separately and to differ from other groups who were even slightly separated. If god was guiding Christianity — if there was a top-down, organizing force — you wouldn’t expect so many irreconcilable versions to spring up. Why can’t Christians agree on basic questions about Christianity?

I’m not so sure Christians want to be drawing attention to the “popularity” of their religion in the first place. The majority of the living human population is not Christian, but the overwhelming majority of all the humans who have ever existed weren’t Christians and didn’t know about Christianity. Less than one third of the current population is not exactly astounding popularity that immediately suggests to me the involvement of omnipotence. Around one hundred billion anatomically modern humans have lived since we showed up fifty thousand years ago, so that means that over 90% never heard about Christianity. Wouldn’t god make himself known and spread Christianity at the beginning of humanity’s existence, not what is probably closer to the end? Why wouldn’t everybody hear what god needed to say, including our very similar ancestors and cousins, who presumably were also made in the image of god? What about the at least five other now extinct species in the homo genus, who lived long before we did and even coexisted with us? Anatomically modern humans have lived for approximately 50,000 years, but our species, homo sapiens, has been around for nearly 300,000 years. This is a serious question that any theist has to answer: What took god so long? If starting his religion was the plan all along, why did he watch billions of humans struggle and die for hundreds of thousands of years before finally doing it?

The Triumph

As we talk about the material causes of the rise of Christianity, all the historical information I’m about to reference — documents, notable figures, etc. — are all coming from The Triumph of Christianity, written by the agnostic historian Bart Ehrman, who you’ve no doubt heard me reference a million times in the last month. It’s linked in the show notes and I’ll be returning to it frequently from here on out.

The Roman emperor Constantine converted to Christianity in 312 CE. This was an important event, but not quite in the way commonly believed. He did not, for example, make Christianity the official state religion. He legalized Christianity after it had been declared an illicit religion for a short time. Under Constantine, Christianity became legal, and even privileged after his conversion. Eighty years later, Theodosius I made Christianity the official religion of the Roman empire and made paganism illegal. So Constantine was the first Christian emperor and he legalized Christianity, and Theodosius I made Christianity the state religion and persecuted pagans into oblivion. The rate of growth for Christianity was such that if it wasn’t Constantine, it would’ve been someone else. It’s not as if his conversion was the make-or-break moment for Christianity, as it’s often portrayed to be. When he converted, Christianity had already grown to a few million followers — nearly 10% of the Roman population. In the U.S., we very nearly had a Mormon president, and Mormons make up about 2% of the U.S. population.

So at this point it’s not all that weird. A small religion has become a bigger religion. The location here is highly relevant — Christianity was very much in the right place at the right time. There weren’t millions of Christians just anywhere — they were in the Roman empire. At the time, the biggest and most dominant civilization, and though it eventually fell, it was a central ancestor to modern Western civilization. But Constantine’s conversion came almost three hundred years after Christianity began, so how did we get to that point?

About half of the Roman empire was Christian by the fifth century, putting the number at about thirty million. No massive conversions were needed for these numbers to be achieved. All that was needed was a steady rate of growth. This can be difficult for us intuitively, since humans aren’t naturally good with statistics or thinking on the timescale of centuries. It’s been calculated that Christianity, starting with about two dozen followers in 30 CE, only needed a growth rate of roughly 30% per decade to reach the levels that it reached. All you need to witness the amount of growth Christianity had undergone from 30 CE to the fifth century is a growth rate of roughly 3% per year, 30% per decade. If that doesn’t sound like a lot, that’s because an exponential curve yields far greater numbers than our intuitions would lead us to believe, and there are plenty of thought experiments that try to help us understand that. There’s the famous example of taking a chess board, putting a single grain of rice on the first square, and doubling the amount of rice for each square on the board (a growth rate of 100%). The first tile has one grain of rice, the second has two, the third has four grains, the fourth has eight grains, and so on. By the end of the board, which has 64 squares, you’re left with 18 quintillion, 446 quadrillion, 744 trillion, 73 billion, 709 million, 551 thousand, 615 grains of rice. That’s slightly higher than what you would expect. The point being your intuitions are not good at estimating the power of exponential growth over a centuries-long timespan. 3% per year is not an implausible or miraculous rate of growth. It wouldn’t even require a concerted evangelistic effort to achieve that rate. You would just need to occasionally convert a friend or neighbor. We should also keep in mind that the social landscape looked a bit different in that culture. If the head of the household converts, his wife and children also convert. If you convince one guy, you gain his whole family as well. Evangelism was less widely practiced by the earliest Christians than by the later ones. Paul was definitely a missionary and thought evangelism was mandated, and his work laid a lot of the theological foundation for Christianity. The character of Christian doctrine probably did a lot to naturally push adherents towards evangelism. Every early Christian believed the end of history was right around the corner. They thought god was going to judge the world and the only ones who would be spared would be Christians. Non-Christians were not going to be annihilated in this destruction of the world, they would go on to be tortured for all eternity in hell. If you cared about your friends and neighbors, you would want to tell them.


Another unique characteristic of Christianity that helped it gain masses of new followers was the emphasis on monotheism. The pagans of ancient Rome were polytheists — they believed in and worshipped multiple gods. According to Christians, your pagan gods were either not real or they were demonic beings deceiving you. Paganism is a bit of a suitcase term that we now use to denote anyone who wasn’t Christian or Jewish, but they did have some things in common. In contrast to Christianity, Paganism was highly inclusive. When pagans found a new god to worship, they just added that new god to their list. There was no pressure to become a monotheist or a henotheist, someone who believes in many gods, but worships one to the exclusion of all others. Christian belief is different, and this difference may have conferred a survival advantage to Christianity. When you became a Christian, you had to worship one god and only believe in one god. That meant that once you converted, there was no room for anything that wasn’t Christian. Pagan systems of belief could absorb any new gods and survived in part because of that flexibility. Christianity, on the other hand, created a zero-sum conflict and tried to win it.

The nature of Christianity created a zero-sum contest between it and other religions, and the paganism in the Roman empire was ill prepared for this conflict. It didn’t really have the theological antibodies to defend against the kinds of challenges Christianity presented. When a pagan was convinced that they should worship a different pagan god, that didn’t mean that all the other gods they had been worshipping had to be abandoned or all the practices they had been engaging in had to cease immediately for the safety of their immortal soul. But if you became convinced by the evangelists for Christianity, the beliefs you had held to before now had one less adherent. Christianity, unlike paganism, was exclusive. Pagan belief was built to coexist, while Christianity was built to eliminate the competition. So it’s kind of a high risk, high reward sort of strategy. You can’t be incorporated into the pagan pantheon of gods, so if you lose, you really lose. But if you win, you really win.

Bart Ehrman writes, “Christianity was the only evangelistic religion that we know of in antiquity, and, along with Judaism, it was also the only one that was exclusive. That combination of evangelism and exclusivity proved to be decisive for the triumph of Christianity. If it had been evangelistic but not exclusive, it may well have gained adherents, but paganism would have remained unaffected. Pagans would simply have begun to worship Christ along with whatever gods they chose. . . . If, on the other hand, it had been exclusive but not evangelistic, Christianity, like Judaism, would have simply been an isolated and marginal religion without masses of adherents. But it gained a massive following. Not at first, but over time, progressively adding to its ranks year after year, decade after decade. As it grew, paganism necessarily shrank.”

So the nature of Christianity gave it advantages in the competition for religious dominance. And it should go without saying that these things were the result of their theological beliefs, not some consciously held strategy that Christians were employing to try to spread.

The Christian Afterlife

The Pagans of that day didn’t believe in anything like the Christian afterlife. They didn’t believe in a heaven or a hell. We write RIP (Rest in Peace) on gravestones, and the Romans had their own common epitaph that had a much more Epicurean view of death. It’s letters stood for, “I was not, I was. I am not, I care not.” Epicurus was a Greek philosopher who argued that it was impossible to experience death, since one has to exist to experience anything at all. He said, “Why should I fear death? If I am, then death is not. If death is, then I am not. Why should I fear that which can only exist if I do not?” Christians came along and eventually started saying something different — you’re never going to die. You’ll get to live forever in paradise if you convert. Also, if you don’t convert, you’ll still live forever; you’ll just be burning in hell. Christians focused on some other, unseen world, and claimed that this was the true world. It’s an easy answer for someone trying to understand the ambiguity, suffering, and injustice that everyone can clearly see. Christians claimed that if you became a Christian, a utopian existence awaited that would last for all eternity. But if you don’t become a Christian, not only will you be missing out on that perfect existence, free from all suffering — you’ll be tortured for all eternity. This was a new idea at the time. At least when you hear it at first, somebody telling you that you don’t have to deal with loss is a welcome message. Not to mention the threat of hell. You’ll see your loved ones again, and all those people you hate will go to hell! Even the other Christians you don’t like will probably go to hell, since they’re Christian-ing wrong. So you have heaven for you and your friends and family, and you have hell for your enemies. And I’m not being unfair in the least by claiming that Christians happily pictured the torments of hell for those who didn’t find them convincing.

The Only Sadistic Literature in the Ancient World

Bart Ehrman writes, “In the second century, accounts of the afterlife begin to appear in Christian texts, often presented as guided tours of the realms of the blessed and of the damned. In these a saint is shown the ecstasies of the saved and, especially, the torments of the lost, presented with barely concealed voyeuristic glee. The Roman historian Ramsay MacMullen has called these accounts ‘the only sadistic literature I am aware of in the ancient world.’”

In a text called the Apocalypse of Peter, Jesus shows the disciple Peter the terrors of hell. Blasphemers are hanged by their tongues, adulterers are suspended by their genitals, doubters have their eyes continually burned out with red-hot irons, women who performed abortions on themselves are buried in excrement up to their necks, idol worshipers are recurringly chased off of cliffs, and slaves who disobeyed their masters have to chew out their own tongues.

The third century Christian apologist Tertullian said, “What sight shall wake my wonder, what my laughter, my joy and exultation? …[T]he magistrates who persecuted the name of Jesus, liquefying in fiercer flames than they kindled in their rage against Christians. Those sages, too, the philosophers blushing before their disciples as they blaze together.”

Celsus, a pagan intellectual, wrote that Christians proselytized successfully because they “invent a number of terrifying incentives. Above all, they have concocted an absolutely offensive doctrine of everlasting punishments and rewards, exceeding anything the philosophers . . . could have imagined.”

Saint Augustine himself said, “Very rarely, no never does it happen that someone comes to us with the wish to become a Christian who has not been struck by some fear of God.”

This was a central argument Christians used. They terrified and threatened people with hell. To quote Ehrman, “Sophisticated argument was almost certainly not the principle engine of conversion.” In addition to appealing to fear, they used arguments appealing to martyrdom (which we talked about last week), and arguments appealing to miracles (which we talked about in the Easter episode and back in episode twelve).

We have a few sources that indicate that the early Christians were not the best and brightest in society. In 1 Corinthians 1:26-27, Paul recognizes the status of most of the believers in the church when he says, “Not many of you were wise by human standards, not many of you were powerful, not many of you were born to nobility. But God chose the foolish in the world to put to shame the the wise; God chose the weak in the world to put to shame the strong.” He’s acknowledging that most of the Christians he’s writing to are uneducated and powerless. About a century after Paul wrote that letter, Celsus, the pagan intellectual, made the same observation. He wrote that Christians were typically poor, unskilled laborers. He also called them “illiterate” and “gullible.” An early fourth century source, written by a Christian defending Christianity, also indicates that most believers were uneducated and “foolish”. No serious intellectuals converted to Christianity until centuries after it began. There were three notable figures who converted around the middle of the second century, but those were the earliest ones, and it took centuries longer for Christianity to gain traction with educated people. The point is that the evidence, whatever it was, was only convincing the least skeptical and least educated people for centuries.


Christianity was different enough to have a competitive edge over it’s Pagan contemporaries. The combination of evangelism, exclusivity, and belief in the afterlife created a religion that, in the context of the Roman empire, propagated very successfully. There is actually not a single thing about the spread of Christianity that can’t be explained naturalistically with ease, once you look at the data. The current number of Christians and the growth rate of the early church, the two most cited facts in this argument, don’t work as objections to naturalism in the slightest. A growth rate of roughly 3% per year is not so miraculous as to defy rational explanation. And less than one third of the human population is not stunning, especially when you consider where Christianity appeared. I don’t think we should even consider this one third to be a figure that Christians should be allowed to point to, since it includes believers and entire denominations that others consider to be heretical. Unless you think everybody is going to heaven  — all the disparate versions of Catholicism and Protestantism, along with the different versions of the Eastern Orthodox church, and all the LDS Christians — unless you think everyone is right, you can’t cite the one third figure. We also shouldn’t lose sight of the fact that the popularity of a belief doesn’t add to the likelihood of that belief, and yet that’s essentially what this apologetic boils down to.

Supernatural explanations can be made, because they can always be made anywhere, but they’re not needed for the spread of Christianity any more than we need supernatural explanations for volcanic eruptions. Not to mention the endless problems that any invocation of divine intervention raises. What took so long for god to do this? Why wasn’t an omnipotent being more successful in achieving his goals? Why are there false religions? Why don’t Christians agree on anything? You wouldn’t expect any of this if Christians were right. An omnipotent god, organizing from the top-down, easily could’ve started Christianity the moment humanity came into existence, instead of tens or hundreds of thousands of years after. He could’ve miraculously spread the Gospel to every place on Earth, but he didn’t for some reason. He could continually prove to us which religion he favors and which ones are untrue. And he could ensure uniformity in the Christian doctrine on the nontrivial matters, so no one could use the true religion to spread falsehoods. But apparently god only intervened enough for a miraculous 3% annual growth rate that resulted in a not quite one third of the population that disagrees with itself to the point of fighting wars over their differences.



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The Triumph of Christianity: How a Forbidden Religion Swept the World — Bart Ehrman [Amazon]

Bart Ehrman Interview [NPR]

Christopher Hitchens [YouTube]

2015 Religious Demographics [Pew]

How Many Anatomically Modern Humans Have Lived on Earth? [PRB]

Your Logical Fallacy Is…


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