The Empire Within the Empire
Around the year 300, Christians numbered anywhere from 5 to 10 percent of the population of the Roman Empire. In some provinces (e.g., Britain), Christians could hardly be found. But they were so numerous in other provinces, their internal disputes endangered the peace of the civic community.
In many Mediterranean lands, Christians had penetrated all levels of society. It had once been said that few Christians were wise by human standards or influential or of noble birth (1 Cor. 1:26), but this characterization was no longer valid. Christianity had become a minority that simply could no longer be ignored. Persecution, far from eradicating the Christian faith, served to highlight its remarkable powers of survival.
Without publicized campaigns or even an explicit evangelistic strategy, Christianity had made its way quietly and effectively in an environment not wholly unlike that in the post-Christian West today. It was, in some respects, an empire within the Empire.
So, how did it grow so large that one emperor felt threatened enough to persecute it mercilessly, and another was intrigued enough to adopt its faith.