This is a good question, one that Brown never adequately answers.  Brown claims that Constantine was a committed pagan who was “forced” to convert to Christianity on his deathbed when he was too weak to resist.  But if this was the case why would Constantine support changing Christianity from a religion that followed the pagan, nature-based teachings of the man Jesus to a religion that worshipped a divine Christ?  Wouldn’t his own religious convictions (as Brown presents them) have led him to keep Christianity as it was?   This is all the more true if, as Brown claims, Constantine was backing Christianity only because he saw it as the horse that was winning.  If the non-divine Jesus movement was winning the day, why would Constantine risk modifying this religion so radically?  The whole story really makes no sense at all.