SO OBVIOUS
Please, gents.
I can't believe none of you have figured out this movie.
There is only one real question:
Who is One Eye?
The answer is breathtakingly simple.
Note:
He is missing his LEFT eye.
He is mute.
He is an unconquerable warrior.
He has visions of the future.
ODIN. That's who it is.
Odin comes down from Asgard to see how his people are faring with the rise of Christianity, and is disgusted with what he beholds. He fights, testing any who might be worthy to reach Valhalla, but finds none - especially among those who watch the gladiatorial combats.
The Boy is the Future. The future of his people lies in North America - and the greatest majority of european immigrants to North America were from Germany and Scandinavia.
That is why the crusaders wind up there. They are also unworthy. The boy, though, endures.
In summary: The film is an allegory of the end of the Viking Age, the rise of Christianity and the discovery of the New World.