Just finished Dr. Rodney Stark's Cities of God: The Real Story of How Christianity Became an Urban Movement and Conquered Rome. Powerful research for anyone striving to become a historically-informed Christ-follower. The results of his studies overturn many long-held assumptions. Some of what I underlined while reading:
Once Christianity became safely ensconced as the Roman state church, its missionary activities very rapidly decayed.
What Christianity offered the world was monotheism stripped of ethnic encumbrances.
Conversion is primarily about bringing one's religious behavior into alignment with that of one's friends and relatives, not about encountering attractive doctrines.
In the United States, the group most likely to convert to a new religious movement consists of people raised in an irreligious or nonreligious home.
Gnostic scriptures far more resemble pagan mythology than the New Testament.
Constantine was not responsible for the triumph of Christianity. By the time he gained the throne, Christian growth already had become a tidal wave of exponential increase.