How did Christianity go from being a small sect in a corner of the Roman Empire in the first century to the religion to which the emperor converted in the early fourth century? Its spread was greatly aided by the political unification of the empire and the extensive road network, as well as by the belief of many Christians that religion was something anyone could embrace, regardless of regional or religious background.
1. Everyday citizens spread the word
Missionaries like Paul, an important figure in the Bible’s New Testament, traveled through the kingdom with the intention of spreading Christianity. However, most people who have helped spread the religion did so only by talking about it with their neighbors, friends, and family members, says Edward Watts, history professor at the University of California, San Diego and author of The Last Pagan Generation: Rome’s Unexpected Journey to Christianity.
“Missionaries are part of the story, but most of the story is about ordinary Christians talking to ordinary people,” he says. “And that, I think, is the single most important reason Christianity emerged the way it did in the Roman world. It’s less the missionary work of people like Paul and more people whose names we don’t know.”
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2. Early on, Christianity coexisted with “paganism”
At the height of the Roman Empire in the second century, it stretched across Europe, North Africa, and the Middle East. One of the main reasons Christianity was able to spread throughout this vast empire was that many people saw the new religion as something they could easily embrace without having to change their existing cultural and religious practices.
In the first and second centuries, most people in the Roman Empire worshiped several gods at the same time. When they heard about Christianity, they didn’t necessarily think that worshiping Jesus Christ meant they had to stop worshiping their other gods like Jupiter, Apollo, and Venus. Rather, many embraced Christianity, adding Jesus to the group of gods they already worshiped, says Watts.
The belief that Christianity was compatible with what we now call paganism helped spread Christianity throughout the Roman Empire. Although some Christians argued that there is only one God and that Christians should worship no other, Watts says many people in the Roman Empire did not understand Christianity that way at the time.
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3. Christianity did not present itself as an exclusive club
Christianity was also buoyed by the idea that it was a religion for everyone – not just for people in a particular region with a particular religious background. Although some Christians debated this point, missionaries like Paul preached that a person need not obey Jewish laws regarding circumcision and kosher dietary practices in order to become a Christian.
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“This is an important change because it lowers the barrier to entry a lot,” says Watts. “If you’re a man who wants to convert to Christianity and there’s an assumption that you have to convert to Judaism first, it’s literally physically painful and dangerous for you to convert.”
In addition, the translation of Christian gospels from their original Aramaic into Greek made them accessible to more people in the empire. Unlike Aramaic, a regional language spoken in Judea, Greek was spoken throughout the Roman Empire.
READ MORE: 8 Ways Roads helped Rome rule the ancient world
4. Early persecution was not widespread
During the first and second centuries, persecution of Christians in the Roman Empire was sporadic and regional rather than empire-wide. The persecution of Christian martyrs like Ignatius of Antioch, who died in the second century, did not represent the experience of most Christians.
This did not change until the mid-third century when the emperors Decius, who reigned from 249 to 251, and Valerian, who reigned from 253 to 260, launched campaigns to promote traditional Roman values and customs such as sacrificing animals to pagan gods . Officials documented these sacrifices with papyrus receipts, which people could keep as records of their sacrifices. Those who did not have these receipts and refused to sacrifice could be arrested and killed.
Decius’ campaign did not target Christians specifically, but anyone who did not practice pagan sacrifice. In contrast, Valerian’s campaign targeted Christians more directly. After that, the next major campaign against Christians was the Great Persecution. From 303 under Emperor Diocletian, this led to the deaths of many Christian religious leaders and the confiscation of Christian property
5. An emperor converted – and officially recognized the faith
The Great Persecution was the most severe persecution of Christians in the Roman Empire – and also its last. Because after this persecution, Emperor Constantine I converted in 312 as the first Roman emperor to Christianity. A year later, he helped enact the Edict of Milan, which ended the government’s persecution of Christians and made Christianity a recognized, legal religion within the empire.
Constantine’s rule did not mark an immediate change in the Roman Empire from pagan to Christian. “It does, however, initiate a process that will lead to the imperial government’s explicit limitation of pagan practices and explicit encouragement of Christian practices by the end of the fourth century,” says Watts.
Christianity continued to spread throughout the territories of the Western Roman Empire after its fall in 476. Over the next several centuries, it became the dominant religion in the city of Rome, as well as in the regions of Europe over which the Roman Empire had ruled. The Roman Colosseum, once the scene of deadly gladiator fights, even became a sacred Christian site where an artist painted a picture of ancient Jerusalem in the 17th century.