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How Many Christians Were There?

There are a lot of things that I’m really very interested in that I’m not very good at.  As a kid I was passionate about baseball.  I was an All Star every year up to high school, but I really wasn’t all that great.  I was just better than most of the other kids, who *really* weren’t great.  It was a rather low bar.  Same with tennis.  Same with a lot of things – even into adulthood.

As an adult I’ve long had an attraction to numbers, but I’m not very good at them.  I’m fascinated by them, but I can’t work out much of any kind of sophisticated mathematical formula to save my soul.  That’s why last week I asked for some help on the blog.  I needed someone to come up with a formula for me to crunch some numbers.   And several people obliged.  Many, many thanks to all who helped.  I’m very much in their debt.  It’s amazing to me the kinds of expertise that are out there.  Some of my respondents were able to answer my questions off the top of their heads.  Unbelievable.

My questions were about the rate of Christian growth, the topic of yesterday’s post.  There I pointed out there that sociologist Rodney Starks, who unlike me is a numbers guy, figured out that if there were about 1000 Christians in the year 40 and about 6,000,000 in the year 300, you only need a growth rate of about 40% per decade to get there.  And that, as it turns out, is the growth rate of the Mormon Church since it started in the 19th century.  (Well, it was the growth rate of the Mormon church up to the time of Starks’s book; I doubt if it’s the growth rate now, since if it were, masses more of us would be Mormon….)  No miracles are needed.  Just steady growth.

There are lots of difficulties with these calculations that I intuited, and now that some of our faithful blog users have given me formulae for doing the math, I can express them concretely.   They have to do with…

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Playing with the Numbers (of Christians)
The Rate of Christian Growth



  1. talmoore
    talmoore  May 16, 2016

    Dr. Ehrman, like most NT scholars, you probably wouldn’t feel comfortable dipping your toes into another faith, but Christianity wasn’t actually the first religion to have (relatively) rapid growth. In fact, there was an historical precedent with Buddhism, the rise of which shares many familiar milestones. The Buddha Gautama Siddhartha also had disciples who propogated his teachings through canonical documents — the so-called Pali Canon. The Buddhists were also known in the subcontinent as ascetics who set themselves apart from a corrupting society. The Buddhists engaged in missionary activities in order to spread The Buddha’s message of salvation — in this case, salvation being Nirvana arrived at through the Four Noble Truths and the Eightfold Path. And, most importantly, Buddhism went mainstream with the conversion of an emperor — that emperor being Ashoka of the Mauryan Empire of India ca. 3th century BCE (about 300 years after The Buddha, just like the 300 years between Jesus and Constantine).

    Now, I’m sure this is mostly coincidental, but the fact that there was a predecent for the (relatively) rapid growth of a new religion, I would think that is significant. Moreover, that it took a conquering autocrat to officially institutionalize each religion into the state I think is also significant. I belive that if you were to delve a bit into the growth of Buddhism from The Buddha’s death to emperor Ashoka, it may give you a better sense of the growth of Christianity from the death of Jesus to emperor Constantine.

  2. Avatar
    thebigskyguy  May 16, 2016

    You can play around with different growth rate scenarios easily using simple financial formulas found in Excel. Just substitute Christians for Dollars (which curiously is, I believe, the motto of the American Tele-Evangelical Association). Assuming monthly compounding in order to approximate a continuous growth rate (as opposed to a very large tent revival held every ten years), it only takes an annual growth rate of about 3.35% to get from 1,000 Christians in 40CE to about 6 million 260 years later. Obviously the required rate of return will be quite sensitive to the starting number (Present Value). If you only start out with 20 Christians in 40CE, it takes an annual growth rate of 7.531%.

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    RonaldTaska  May 16, 2016

    You may not have made it to the major leagues in baseball, but you sure have made it to the majors in your chosen field. So, the growth of Christianity does not depend mostly on Constantine. Interesting for me to let go of still another myth lodged in my brain. That is what this website does and that is a good thing.

  4. Avatar
    JR  May 16, 2016

    I think persecution does often cause growth. I have it on good authority that the underground church in China is huge. This despite the government’s continued persecution for many years. And you hear people use the expression ‘don’t make a martyr of him’ insinuating that punishing someone will spur on others associated with their cause. Punishing extremists can lead to others being radicalised. Maybe there is something about humans that makes us rise to a challenge.

    • SBrudney091941
      SBrudney091941  May 23, 2016

      Maybe, but, as you point out, they are underground and so wouldn’t be persecuted that much–even if they had been early in the movement. And, if the government doesn’t want to make martyrs out of them, then they probably torture or execute them in secret, not in public so that you would have, not public spectacle, but missing Christians.

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    Michael Fischer  May 16, 2016

    I believe it is still important to point out that the rate of growth is smaller than the rate of conversion. Also, would you say that the growth rate post Constantine’s conversion does not necessarily reflect a less convincing Gospel, due to there no longer being persecution, but just a more Christian context? If 50% of the people around you are Christian then you convert less people than if it were 1%.

    • Bart
      Bart  May 17, 2016

      Good point! But explain how you understand the relationship between rate of converstion vs. rate of growth (which obviously, you’re right, are not the same thing)

      • Avatar
        josephatalla  June 24, 2016

        I am actually looking at the same thing, according to resources specifically by Scott Manning, the average total world population at year 30 was 246,639,657, and at year 300 the average population was 264,410,429. I analyzed the growth rate from year 30 to year 300 and found that the average yearly growth rate between 30AD to year 200AD was about 0.03% and the average growth rate between 210AD to 300AD was 0.017%. As we can see the population growth rate is so small, even if we use 1% growth rate for 1000 people after 270 years these 1000 people will number only 14,681 which is not significant enough to be considered. You can comfortably eliminate the population growth rate and focus on the conversion rate.

        Now as far as conversion, I know the bible is not a reliable historical account, but Jesus fed over 5000 people at one time and he was going all over Palestine preaching. The Pharisees and Pilate wanted Jesus dead since he had many followers and caused a direct threat. I would think that 1000 Christians by the year 40 is probably a bit low. I also, believe conversion rate is definitely not linear and depended on many factors, such as life span, population density, geography, socioeconomic, culture, politics, Emperor Constantine, and obviously competition between other religions. Christianity brought something new and convenient which allowed the governments to better control the divisions among its people. The idea of oneness to pagan Europe, African and Asia Minor was attractive, at the same time the flavors Christianity offered helped assimilate the religion into the Pagan Culture. Christianity offered, Man who became God, a God who became man, a virgin birth, one God and three Gods. Something for everyone!

  6. Avatar
    Pattycake1974  May 16, 2016

    If the number of persecuted Christians has been exaggerated, it would be helpful to know how many were actually persecuted and if it impacted growth when reading your book.

    I understand your point that steady growth does not equal a miracle.

  7. Avatar
    Wilusa  May 16, 2016

    “You need a steady rate of growth. That’s a completely feasible one for a missionary religion.”

    Yes, *if* the missionary religion appeals to people. What do you think were its most important “selling points”? I’d guess its promises and threats about the afterlife…but why did people find them particularly *believable*?

  8. Greg Matthews
    Greg Matthews  May 16, 2016

    I think there’s something important here that isn’t being mentioned: plague. Most people only know about the Black Plague, but there have been many documented plagues going back to the beginning of recorded history. Off the top of my head there was a major one during the reign of Justinian, but that’s from the 500’s; and, there was an earlier one during the reign of Marcus Aurelius (2nd century) that supposedly killed 1/3 of the population in *some* parts of the Roman world. There were probably other smaller regional plagues between 40AD to 300AD that I don’t know about, but just taking into account the plague I mentioned, how does that affect the numbers?

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    Todd  May 16, 2016

    The numbers are interesting. If there were that many one would surmise that they could not practically keep their affiliation to the curch a total secret.

    What I am most interested in is the contextual ethos of life as a Christian in the early years…where they lived, occupations, places of worship, how they brought in new members, how there beliefs changed through the years (and what those very early beliefs were).

    I realize that such information may be impossible to find in any abundance, but such would be very enjoyable to read.

    Hope you can add a bit of that too.

  10. Avatar
    chrispope  May 16, 2016

    I don’t know if this point has already been made. If it has, I apologise.
    In some societies at some times, and in some societies in current times, the head of household determines the religion of the household. So a converting ‘head of household’ could bring with him quite a number of ‘Christian adherents’ – family, sevants/slaves, etc. The individual faith of some of those ‘brought-in’ adherents may have been shaky, but they probably would have counted as ‘Christians’. Thus it may not always have been a question of one conversion at a time.

  11. Avatar
    Stephen  May 16, 2016

    I’m fascinated by your starting figure of 20 people. I assume you mean the hardcore followers, the immediate disciples and others willing to pack up and move from Galilee to Jerusalem. But if we accept that Jesus had some sort of Galilean ministry of indeterminate length wouldn’t it be reasonable to suppose that there might have been a group of followers who remained behind when Jesus and his immediate disciples went to Jerusalem? Don’t we have hints of this in Mark, Matthew and John when Jesus instructs his disciples to meet him in Galilee after the resurrection?


    • Bart
      Bart  May 17, 2016

      Yes, I assume some of these would have converted soon after some of the 20 told them about the resurrection.

  12. Avatar
    gabilaranjeira  May 16, 2016


    But if we question the initial 1000 don’t we have to question the 10% by end as well? How do we know that was the right estimate?


    • Bart
      Bart  May 17, 2016

      There seem to be pretty good reasons for thinking that 5 or 6 million were Christian by the time of Constantine; these are guesses, but they are based on some data and most experts who really delve into it seem to agree….

  13. Avatar
    gabilaranjeira  May 16, 2016

    I have another question:

    Even if Constatine isn’t necessary to explain mathematically the rate of Christianity growth, wouldn’t his conversion still be decisive in a civilization that did not separate state and religion? Obrigada!

    • Bart
      Bart  May 17, 2016

      I think his conversion certainly made other conversions much easier!

  14. Avatar
    godspell  May 16, 2016

    Yeah, statistical analysis alone won’t cut it. For one thing, other religions were seeking converts–all they had to do was the same thing. Christianity was clearly doing a more effective job of reaching people who weren’t already strongly committed to another faith.

    And how much do we really know about how strongly people were committed to the mainstream pagan practices? There’s been some scholarship on this, but I get the impression there are a lot of gaps in our knowledge.

    It seems like most religions that make it have an early growth spurt, then level off–barring some outside factor, like Constantine’s conversion, or the Islamic jihads (or western colonialism in the 19th century).

    In talking about why Christianity spread, you also have to talk about why paganism declined, and Christianity itself can’t be the only reason–neither can Constantine’s conversion. Because he couldn’t have converted simply because of a dream. He must have seen some energy in the new faith he wasn’t seeing as much in paganism.

    A crisis of confidence in the Roman order–which Roman paganism symbolized, as the state religion–could have spurred people to seek solace elsewhere. Then Christianity became a state-sanctioned religion–acceptable to a greater variety of people, but perhaps losing some of its early anti-establishment allure in the process. People would start joining for reasons that had nothing to do with belief.

    • Bart
      Bart  May 17, 2016

      Which other religions were seeking converts?

      • Avatar
        godspell  May 17, 2016

        The Mystery Cults–more exclusive, perhaps–but obviously they did seek initiates, or we wouldn’t even know about them. The much-touted Mithras Cult. The Cult of John the Baptist, that Christians were so concerned about, they wrote stories into their gospels showing John accepting Jesus’ supremacy.

        There’s a lot we don’t know, but that being the case, it hardly seems prudent to assume that only Christians were out there proselytizing. That seems highly improbable. Where there’s one, there’s more.

        • Bart
          Bart  May 18, 2016

          Yeah, you might think they were out seeking initiates, but so far as we can tell they were not. There weren’t any missionary religions among the pagans that we know of. People were *attracted* to the Mysteries because of what they had heard about them; but there weren’t any missionaries or evangelists. If you want to read a full study that gives all the data and an informed discussion, see Martin Goodman, Mission and Conversion.

          • Avatar
            godspell  May 18, 2016

            “Far as we can tell” leaves a fair bit out. Why do we know about Christian missionaries? Because Christianity survived, and left a written history behind it. Christians were people of the written word–that’s an advantage they had that most pagan faiths did not.

            I know my own pagan ancestors in Ireland didn’t write down their sacred stories–even though they had a system of writing used for commerce and such–because that was taboo. They were only passed on orally. We only have their stories today because of Irish Christian clerics writing them down (with the odd Christian gloss that can easily be distinguished from the original story). Christianity is actually the main reason we still know anything about the old pagan religions. They were mainly not very good at documenting themselves.

            I don’t see how the cult of Mithras could have spread so quickly just by word of mouth. Or how the Cult of John could have been enough of a threat to Christianity for stories about John’s submission to Jesus being written into the gospels. I would agree Christianity had a superior system of proselytization, that they worked harder at it, but the absence of evidence of missionary activity from cults that didn’t tend to leave a written record of their activities–not good enough to draw a firm conclusion that they were not out there actively seeking converts. They were clearly not doing it as well. But Christianity had plenty of rivals.

          • Bart
            Bart  May 19, 2016

            We do have written records of other Roman religions — it was a topic of broad discussion. (But on your first point: One of the surprising things about early Christianity is precisely that we *don’t* hear of missionaries, after Paul.)

          • Avatar
            godspell  May 19, 2016

            We have written records of the official state religion, obviously. That was much more a matter of politics than of faith. Christianity would take on many of its aspects after Constantine.

            But I think a line needs to be drawn between the gods the people were actively encouraged to worship as a sign of loyalty to the state, and what could be termed popular or folk religion. Christianity was one of those, but different–the others could go along with the state religion without really being part of it. Jews were allowed to not sacrifice to the Roman gods, because they managed to somehow make it clear they were different, apart. Christians were originally perceived as a different variety of Jews, but once they started converting Non-Jews–including in some cases, the children of the patrician class, that wasn’t going to work anymore.

            Pliny the Younger’s letter to Trajan proves two things–first that the Empire tended to deal with Christians on a sort of case-by-case way, without any systematic effort to stamp out the cult, which as you say elsewhere, was not perceived as being so very important. But it also proves that to be a Christian at that time meant that without any advance warning, you might be forced to choose between your beliefs and your life.

            There are people living in the world today who know what that’s like. But have you ever met one? I haven’t. Do you wonder what that’s like? How you might have chosen? I do.

      • Avatar
        Rogers  May 23, 2016

        Mani’s religion was missionary and had significant growth in its heyday

  15. Rick
    Rick  May 16, 2016

    Dr. Ehrman,
    This has been fun. I started out with an Econ Major and it was fun drawing curves and such – until I hit the point where they expected me to apply that 15 hour of C in Calculus I had suffered through… So much for the story of why I am a CPA.
    A few thoughts…
    1. If I recall, time series data of social phenomenon almost always has a relevant range – outside of which – while it may be interesting that e coli unbounded by nutrient media will bury the earth in slime in a few weeks…it is only good for a laugh.
    2. Dr. M.D. (Mad Dog) Anderson at the University of Florida in the 60’s ranted about “co-curvilinearity” – or just because you can fit a function to data with a high coefficient of regression – doesn’t mean there is real causality until you can explain the causal mechanism. To that end..
    3. Would not the exponential imply, or assume, that each Christian and Christian convert was an equally successful evangelist? Since that is unlikely to the extreme – as you note the growth rate was probably variable – the growth is probably not a function and almost certainly is not really an exponential. Would that not then detract from the implication that Christian growth was extraordinarily tied to the Christian message? In other words, the message was not so compelling that every convert devoted himself to evangelism and (because of the message) was also successful at it.

    • Rick
      Rick  May 16, 2016

      Which then leads to the supposition – if not the message, perhaps it was the messengers?

    • Bart
      Bart  May 17, 2016

      Interesting points. On #3 — no, it would only mean that a small percentage were good evangelists. If growth rate is only 3% per year, then only 3% of the Christians need to convert someone that year!

  16. Avatar
    bmacrae  May 17, 2016

    Have you looked at a logistic growth model? My understanding of this model is if plenty of people are available to convert, then growth rate is high, but as the general population becomes more saturated with Christians the growth will slow and eventually stop. In its simplest form I think it can be a linear regression from a high growth rate to a low growth rate. I tried a few numbers (I am no expert), by starting with a growth rate of 60% per decade in 40CE and reducing each decade (linearly) to a 5% growth rate per decade in 380CE, then starting at 1000 Christians 40CE, I got 6.5million at 300CE (still growing at 18% per decade) and then around 14million 380CE (25% of the population). Adds more variables, which is problematic. Suspect it is also still too simple.

  17. Avatar
    plparker  May 17, 2016

    Isn’t Christianity the only major religion that has a missionary focus? It seems to me that’s an important factor in assessing growth rates too.

    • Bart
      Bart  May 17, 2016

      It was the only one (we know of) in antiquity!

    • Avatar
      GregAnderson  May 29, 2016

      plparker writes: “Isn’t Christianity the only major religion that has a missionary focus?”

      With respect, I hear this claim often, but it never makes any sense to me. About the same time Christianity was spreading all over the Roman Empire, some other folks were building underground temples with some rather strange artworks depicting the sacrifice of a bull (yes, I’m talking about Mithraism here). We’ve found hundreds of these temples in every corner of the empire. The art in each follows consistent patterns of iconography, suggesting some sort of communication from temple to temple (books are not the only means of disseminating culture).

      We don’t have any texts describing the work of Mithraic missionaries (that I know of), but we don’t have any texts describing anything else about the religion either (or very little). Somehow, however, the faith grew and spread. That much is undeniable. And understandable.

      If I imagine myself a 1st century pagan, and I’ve got some problem I need solved, I might pray and bargain and sacrifice to a particular god or goddess. And if that problem happens to go away, as if by magic, well … I’m going to tell all my friends and family the good news. That’s just the kind of guy I am.

      No great missionary zeal is required to create slow, steady growth over a long period of time.

  18. Avatar
    DeanMorrison  May 17, 2016

    Hi Bart – models of exponential growth are really too simplistic an approach. They fall down for the same reasons that pyramid selling schemes don’t work. For.example if you think of the rate of growth in a town of say 1000 people. A 40% rate of growth would initially increase converts rapidly. But fairly soon that rate would start to decrease – new converts would find themselves quite literally ‘preaching to the converted’, and would be unable to achieve the growth rates of the first initiators.

    Biologists studying the spread of introduced organisms or diseases take a population biology or epidemiological approach, and there’s no reason at all not to apply this to the problem you are studying. It won’t help you a great deal with exact numbers, but it may open some new lines of thinking for you.

    A population biologist would look at a number of factors in order to build a model – things such as:

    Recruitment Rate
    Mortality Rate
    Immigration Rate
    Emigration Rate
    Size and susceptibility of potential host population
    Demographics of host population
    Development of resistance

    The fast growth and continuing growth of Mormonism (beyond Utah anyway, where they long ago reached the point of preaching to the converted) probably has a lot to do with:

    a) heavy investment in missionary work
    b) that they do this with young people, who are then probably committed to evangelism for a lifetime
    c) that they do so by sending out missionaries in pairs, in order to minimise ‘mortality’ rates – so if one if the pair is tempted to lose the faith when they are away from home, the other is on hand to hold them back.

    This wikipedia article summarises the field:


    But I’d suggest first you could have some fruitful discussions with your colleagues in the ecology and evolution department at your own university:


  19. Avatar
    Triassicman  May 17, 2016

    How does the birth and death rate feature in this? How many children per family and did children generally follow their parents religions? Do we know the population increase per year at all?

  20. Avatar
    dragonfly  May 17, 2016

    I find these figures problematic. It sounds like Christianity was growing at 40% per decade before Constantine and 17% after. Obviously that can’t be right. This is how I see it. If we accept the 17% after Constantine, we need to assume the same or less before. If we accept an average of 40% per decade for the whole of the period up to 312CE, then clearly the decade leading up to that was way under the average, which means at some other point it was way over the average. I think the very start was the point of the highest conversion rate. Let’s say within weeks of Jesus death 10 people believed he had been ressurected, let’s count them as Christians. Then each one convinces their spouse, that’s 20, a 100% increase straight away. Then that year each couple convince 8 others, that’s 100 in the first year, a 1000% increase on the initial 10 in just one year. For the next 9 years, every 10 Christians convert 3 people a year. That gives us our 1000 in the first decade. I think these figures are *very* conservative.

    • Bart
      Bart  May 18, 2016

      Yes, you’re right no one thinks that there was a steady rate of growth up til 312 and then another steady rate after 312!

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