When in 313 the emperor Constantine declared his support for the Christian religion, he was taking a risk. An earlier generation of church scholars had supposed that in the three hundred years since the death of Christ, his followers had manage to expand to the point that Constantine's declaration of support was simply a recognition of the inevitable--Christian triumph by sheer force of numbers. Recent work suggests a more complex reality. Christianity was very slow to get going: by about 200, perhaps as many as 200000 Christians existed on the earth. Even by maximum estimates of expansion, Christian populations in the early years of the 4th century probably totaled only about 6 million, perhaps as much as 10 percent of the Roman population. That 10 percent was unequally distributed: in cities, particularly in Rome and the big cities of the eastern empire, and among the poorer and, above all, more middling classes--merchants, lower-level bureaucrats, soldiers, and their wives-- who aspired to rank and prosperity. Christianity had more limited progress among the senatorial elite and in vast expanses of the countryside where about 90 percent of Romans lived out their lives as poor farmers. By 313, in other words, Christianity had a notable presence among urbanites climbing the social ladder, but among both old aristocratic elite and the rural majority the new religion was a vague form on a distant horizon. Constantine's support of Christianity in 313 was no capitulation to an inevitable surge of Christians, but rather a gamble, not only on a faith but also on a class of people on the move.