In Norse mythology, the cosmos or universe was divided into nine realms on three planes held apart by a giant tree, Yggdrasil. The highest plane held the realm of Asgard, inhabited by the warrior gods, the Aesir. Located nearby were warriors slain honorably in battle who inhabited Valhalla, feasting while awaiting the final battle of Ragnarok. On the same plane was another realm named Vanaheim, also close to Asgard, but the fortress home of the fertility gods, the Vanir, who later combined with the Aesir forming the pantheon of Norse deities. Last of the Norse realms upon the highest plane in Yggdrasil, was Alfheim, the realm of the light elves. The Bifrost was a fiery rainbow bridge connecting the upper plane of and realm of Asgard to the lower plane and the realm of mortals, Midgard. Midgard, the realm inhabited by mortals was located below Asgard and Alfheim. Still held in the branches of Yggdrasil, Midgard was bound by seas, encircled on the furthest edge by the giant serpent, Jormungand. Located on the same plane as Midgard but beyond the seas and the encircling serpent was Jotunheim, the realm of the giants and enemies of the gods. Beneath the surface of Midgard, inhabiting the underground tunnels was Nidavellir, the realm of the dwarves. Deeper below Nidavellir and further beneath Midgard was the realm of the dark elves, called Svartalfheim. On final plane beneath the roots of Yggdrasil in a realm of ice and mist was Niflheim, the location of the citadel Hel and inhabited by the dead. The ninth realm was Muspelheim, land of fire and chaos inhabited by Surt, who according to Norse legends, destroys the Aesir, un-making the universe at the final battle of Ragnarok.