Norse mythology revolves around an ever green ash tree of prodigious dimensions, on which the universe is supported, Yggdrasil. It is the axis of the world, the mighty ash, the giver of life and immortality, though there is no myth which described the creation of Yggdrasil. Yggdrasil probably means Horse of Ygg, one of Odin’s names. He was said to have hung in agony from the tree, to gain power over the runes, which brought knowledge to those who could interpret them.
The great ash tree held together the three planes that made up the world. On the first layer were the worlds Asgard, Vanaheim and Alfheim. On the second layer were Midgard, Jotunheim, Nidavellir and Svartalfheim. On the third and bottomost layer were Hel and Nifelheim. The tree passed from the depths of the underworld through the world of men and into the sky, overshadowing the halls of Valahalla.