in a real and meaningful sense, what conservatives like o'reilly and peterson (and i guess fake nazis like spencer) are doing when they talk about this myth of a christian europe is projecting the fantasy of leo III for a return of the empire, based on christian foundations that no emperor before 476 ever actually had. it's both a revision of a history before dec 25, 800 and a projection of a history from that vantage point of standing in rome on dec 25, 800.
the o'reilly-peterson concept of christian europe is the history of europe as leo III imagined it on that distant saturnalia feast day, but as it never actually happened.