The movie, "The 13th Warrior" is based upon Michael Chriton's novel Eaters of the Dead:
"On the very outside, EotD is a retelling of the Epic Poem of Beowulf, the only early Germanic epic left, conceived and written by Crichton on a dare that he couldn't make so-called boring history texts interesting. It took him quite a while to find the correct context for the story, not an amazing fantasy epic, but events that could have been real, that over centuries of embellishment became a tale of great heroic deeds. This context is based in part on actual fragments of a document, written by Ibn-Fadlan, an ambassador of the Caliph of Bagdad in the 10th century. In fact, the first three chapters of the book are a slightly modified rewriting of the Ibn-Fadlan fragments. Crichton then continues the story in the same style. It is told from Ibn-Fadlan's perspective, along with the footnotes one would expect from a scholarly examination of an ancient document."