How Many Christians Does it Take . ..?
How do historians estimate the number of Christians in the earliest centuries? In a previous posting I commended Thomas Robinson’s new book here, in which he shows how the numbers often used by historians don’t “add up.” But a comment asking how historians arrive at their estimates prompted me to this posting.
I think that one factor is Constantine’s adoption of Christianity in the early 4th century. The implicit or explicit assumption is that for him to have seen this an advantageous action Christianity must have been fairly successful already. It is often assumed that a growth comprising perhaps 10% of the population would have been necessary for Christianity to have attained such credibility for Constantine to have adopted it.
Now it is also necessary to estimate the population of the Roman Empire, and estimates vary widely, but something close to 60 million is frequently cited. So, 10% Christians would = about 6 million Christians by about 300 AD.
In short, this is all very rough and ready estimates or scholarly guesswork. (But it’s scholarly guesswork!)
A recent comment posed a good additional question: How many Jesus-followers were there at the outset, in the earliest years after Jesus’ crucifixion? One could infer from the Gospel accounts that Jesus had aroused a certain number of followers during his ministry, perhaps especially in Galilee. These would be additional to the more well-known group of followers who seem to have (re)located to Jerusalem.
From Paul’s reports of his own early efforts to “destroy” (his word) the young Jesus-movement, one could infer that, already within the first year or two, it had become highly visible, and generated the rather harsh verdict reflected in his efforts. Perhaps, as well, the Jesus-movement had already begun to grow impressively, and this, too, was a factor that generated the concern of this then-young Pharisee.
From a very early point, also, the Jesus-movement was trans-local, with followers mentioned in Damascus and Antioch, and probably other places as well. So, it is possible that what became “Christianity” was, from a very early point, a rapidly spreading movement. But it appears that across the second and third centuries this growth continued, with impressive cumulative numbers.
Tertullian (ca. 200 AD) claimed an “immense number of Christians . . . almost all the inhabitants of your various cities being followers of Christ” (Apology 37), and that “our numbers are so great–constituting all but the majority in every city . . .” (To Scapula 2), and that pagan critics “groan over the increasing number of the Christians” (Ad Nationes 1). This may well be deliberate exaggeration for rhetorical effect. But it would have been somewhat counter-productive to make such claims if the number of Christians had been totally insignificant. So, I think that it is likely that, at least in some areas (such as North Africa, where Tertullian lived), Christians were sufficiently numerous to be rather highly visible and of concern to pagan opponents.
Why people joined the Christian movement in this period, given the social costs involved, is the question I urge that scholars should consider more closely in my recent book: Why on Earth did Anyone Become a Christian in the First Three Centuries? (Marquette University Press, 2016).