Which shows that he didn't do his research, since Xianity didn't cause the fall of Rome, it held it off for a while.
I've had more fun working on an alternate that I plan to write some day, where the Isis-cult became Rome's State religion. Both Isis and Xianity were minority secret cults in Rome - the Isis-cult were the "foolish women who offer cakes to the Moon" that Paul attacked - but Paul turned his cult into a mass movement with political clout. If the Isis-cult had had the charismatic preacher instead, your hometown church might be dedicated to the Great Goddess.