Well, HerenIstarion beat me to it. I agree with him. I know for certain in Western culture, not only just Norse, but in others, including Celtic cultures our world was called Middle Earth or something to that effect. The world of mortals was always seen as a world between worlds. We were not in the golden realms of the Gods, nor in the world of the dead, therefore we were in the middle. It is simply something all European peoples have in common. So to sum it up in two words I would say, Cultural Expression. It is the way we saw (or how some of us still do
) the world. It's that simple.
~ Glofin