Medieval Norwegian literature is closely tied with medieval Icelandic literature and considered together as Old Norse literature. The greatest Norse author of the 13th century was the Icelander Snorri Sturluson. He recorded Norse mythology in the form of the "Prose Edda", a book of poetic language providing an important understanding of Norse culture prior to Christianity. He was also the author of the "Heimskringla", a detailed history of the Norwegian kings that begins in the legendary "Ynglinga saga" and continues to document much of early Norwegian history.