The Rise of Christianity, (subtitled either "A sociologist reconsdiers history" or "How the Obscure, Marginal Jesus Movement Became the Dominant Religious Force in the Western World in a Few Centuries", depending on the edition) is a book by the sociologist Rodney Stark, which examines the rise of Christianity from a small movement in Galilee and Judaea at the time of Jesus, to the majority religion of the Roman Empire a few centuries later.
Stark argues, that contrary to popular belief, Christianity was a movement not of the lower classes and the oppressed, but of the upper and middle classes in the cities and of Hellenized Jews.
Stark also discusses the exponential nature of the growth of religious, and why hence the speed of the rise of Christianity is not as miraculous as might be thought.
Stark points to a number of advantages that Christianity had over paganism, to explain its growth: Christians were more likely to survive in times of plague, due to their care of the sick; Christian populations grew faster, due to the prohibition of abortion, infanticide and birth control; in Christianity women outnumbered men, while in Paganism men outnumbered women, leading to a high rate of secondary conversion.
Stark's basic thesis is that ultimately Christianity triumphed over Paganism because it offered its followers a better and at times longer life.