For more than 150 years after the Resurrection, Christians had no official church buildings. During this time, evangelism was conducted mainly in homes, in the context of worship and Christian education. Itinerant evangelists were rarely found in the early centuries.

In Roman society, it was generally expected that everyone would participate in a cult, but few people thought it necessary to believe in pagan gods, like Mars or Venus. The satiric Roman poet Juvenal wrote, "These things not even boys believe, except such as are not yet old enough to have paid their penny for a bath."

At the end of the second century, nearly every popular religion—especially Mithraism—aligned itself in some way with solar monotheism. Thus Christians often talked of the similarities and differences between the sun god and the Light of the World.

Apologists attempting to defend the truths of Christianity sometimes argued with a uniquely Roman mind. Clement of Rome (died c. 97), for example, tried to prove the Resurrection by comparing it to the story of the phoenix—a mythological bird alleged to be reborn from its ashes every 500 years. Clement wrote as if all reasonable people believed in the phoenix story.

Christianity, when it eventually prevailed, often "baptized" paganism: it established churches on old shrines, like the churches of San Clemente and Santa Prisca in Rome. The Church of Santa Pudenziana in Rome is named, not after a martyred Christian (as the legend goes) but after the Roman senator, Pudens, who originally owned the land.

Constantine's famous Edict of Milan, which officially ended persecutions and granted certain favors for Christians, was not an edict (but a letter from a governor), nor was it issued at Milan (but at Mediolanum).

In 250, after over 200 years of evangelistic effort, Christians still made up only 1.9 percent of the empire. By the middle of the next century, though, about 56 percent of the population claimed to be Christians.