In Norse mythology, Bifröst, also called Bilröst, is a burning rainbow bridge that reaches between Midgard (Earth) and Asgard, the realm of the gods. The bridge is attested as Bilröst in the Poetic Edda, compiled in the 13th century from earlier traditional sources; as Bifröst in the Prose Edda, written in the 13th century by Snorri Sturluson; and in the poetry of skalds. Both the Poetic Edda and the Prose Edda alternately refer to the bridge as Ásbrú.