Christianity’s Rapid Growth in the Roman Empire Explained

burgeoning religion spread exponentially, leading to incredible numbers

By Jonny Lupsha, Wondrium Staff Writer

In its first 300 years, Christianity went from 20 followers to several million. This is no small feat considering its competing religions and the limitations of communication. How did it spread so quickly?

Historians estimate that by the year 300 CE, Christianity had grown from a couple dozen followers to at least two or three million if not four or five. It goes without saying that the world had no rapid mail system at the time, much less phone calls or digital methods of communication. Its spread was so fast that some have literally called it a divine miracle, while others claim that thousands at a time undertook mass conversions and renounced paganism.

However, neither option is grounded in evidence. In his new video series The Triumph of Christianity, Dr. Bart D. Ehrman, the James A. Gray Distinguished Professor at The University of North Carolina at Chapel Hill, explains how it really happened, despite some setbacks.

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Taking a suggestion from sociologist Rodney Stark’s book, The Rise of Christianity, Dr. Ehrman uses the statistic of 1,000 Christians in 40 CE, roughly a decade after Jesus’s death, and that of the standard estimate of five to six million Christians in 300 CE. These two figures and dates provide bookends to the major spread of Christianity. How fast, he asks, does the church need to expand to achieve those numbers?

“It requires a completely believable and achievable rate of growth of about 40% per decade,” he said. “That is, if there are 100 Christians this year, in 10 years they need to grow to 140. That means, basically every year, the 100 Christians among them as a group need to convert three or four people. That’s all.

“If every 100 Christians do that, year after year, after 260 years, they have grown from 1,000 people to five or six million.”

In a way, Dr. Ehrman said, it’s like the spread of a disease. If one sick person infects two, and each of them infect two, eventually it becomes a global pandemic. This is because the rate of growth, at a steady factor, inclines on an exponential curve.

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“In the ancient world, the male head of the household—the paterfamilias—determined the religion of the house,” Dr. Ehrman said. “If a man was married with two children, and he converted to the Christian faith, he would make his family also accept the new religion. With one convert, you got four. Even if [the others in the family] do have qualms, they are practicing Christianity rather than some other religion, and so demographically they count.”

Additionally, Dr. Ehrman said, if they continue to practice for the rest of their lives, they almost certainly will begin to accept Christianity, if not fully embrace it as truth. Therefore, for generations to come, the family will likely remain Christian. Even more interesting is the fact that much of this conversion happened without missionary work.

“In the 260 years between Paul and Constantine, there basically was no organized missionary work at all,” he said.

So how was Christianity circulating if not through missionaries? The answer is social networks—not the online kind of course.

“Christians, like everyone else, had connections. You have a family, you have neighbors, you have a town, you belong to organizations, you meet people in the store, you’re familiar with the parents of other kids. Ancient people had the same thing; people in the ancient world talked about religion.”

Christians spoke with people in their various social networks and they would convert some, almost all, through word of mouth. This happened in urban areas especially, with dense populations who weren’t distracted by reality television and video games but were outside talking to their neighbors.

And so, as the saying goes, “word of mouth” spreads information.

This article is part of our “Deeper Dive” series where we examine the stories behind our Wondrium Shorts on YouTube.

Edited by Angela Shoemaker, Wondrium Daily

Edited by Angela Shoemaker, Wondrium Daily