Lol, the show has already "stretched" history in several ways. It turns out that Ecbert never met that King from Northumbria in actuality nor were they even Kings at the same times in History. I wont say what happens in Paris tho History has already recorded it. Watch the show.
There is a whole lot that isnt written in History, or, written in different accounts. Ecbert has some bad times ahead, even tho he becomes the most powerful King in England first. Maybe Ragnar has something cooking that will geld his power, which actually did happen. I wont say more but I think theres enough "flex" in the recorded history to tell a great story. It was a long time ago and wasnt recorded as well as the Roman period. Ecbert, rightfully, admires the Romans.