What is the importance of the Ibn Fadlan Manuscript in the novel, Eaters of the Dead: The Manuscript of Ibn Fadlan?

The Ibn Fadlan Manuscript is a historical document. Michael Crichton did not entirely make up the manuscript or its author. However, Crichton does note the manuscript material makes up only a bit of the first few chapters and then he takes over, writing in the same style as Ibn Fadlan. Ibn Fadlan did not actually travel with the Vikings and there is no known record of Buliwyf or any person resembling him.