Beowulf was written for an Anglo-Saxon audience and contains many elements that are foreign to the readers of today. The 13th Warrior was written as Eaters of the Dead, by Michael Crichton, in the 1990's.
The saga of Beowulf contains many examples of the pagan concept of Wyrd of fate. Both Beowulf and the 13th Warrior are adventures of a hero whose actions determined a nation's fate. In the book, Beowulf was traveling from home to save a nation from Grendel and his equally ferocious mother. In the movie, Buliwyf single handedly kills the head warrior of the opposing enemy. He also ventures into the cave and kills the Wendol Priestess. As the lead-wendol represents Grendel, the Wendol Priestess represents Grendel's mother. The fire-worm from the movie, also symbolizes the dragon from Beowulf. .
Both the epic poem of Beowulf and the movie The 13th warrior hold some form of supernaturalism. The book stated that Grendel and his mother made a spell preventing natural, man-made weapons from harming them. In the movie, the most supernatural thing is the mystique of the bear to create the illusion that the Wendol were in fact more powerful than they truly were. The supernatural thing about it was that the Wendol actually thought that they were bears. When they were in the cave near the Wendol priestess they were chanting. This, as they thought, gave them a supernatural power that was unmatchable. .
Another comparison is the fact of Good vs. Evil. In the book, Beowulf's enemies were portrayed as the known evil throughout and Beowulf was known as the warrior and savior so to speak. In the movie, the Wendol were the "evil" and Buliwyf and the other 12 warriors were the "good." The fire-worm in the movie, which was actually just the fire from the sticks carried by the Wendol, represented the dragon from the epic Beowulf. Another aspect of these was the Good of the Community vs. personal Greed.