Christianizing the Roman Empire A.D. 100-400 by Ramsay MacMullen

Ramsay MacMullen an historian of ancient Rome examines the Christianization of the Rome world. Prior to 313 A.D. with the Edict of Milan Christianity had not been tolerated in the Rome Empire yet a great mass of people still became Christians over a half a million in each generation from the end of the first century up to 313 A.D. 

MacMullen concludes that one of the primary reasons the pagans of the Rome Empire converted to Christianity was because of the supernatural elements of Christianity such as miracles, healings and confrontation of demon spirits. After Christianity became tolerated in the Rome Empire many turned to Christianity because of the advantages of being a Christian.