Just as there were many references to the mythic tales of Durandal littered throughout the Marathon series, it's the ending of Halo 3 that truly cements its mythic ties, aside from the entire build upon the mythology of the Arc of the Covenant, and the references found in the terminals (Marginot line is mentioned... very interesting).
In the end, after the credits, Master Chief puts himself into cryostasis to be awakened when Cortana has need of him again. This is a direct reference to the story of Ogier the Dane, the Danish king who fought and fought alongside Charlemagne the Frank in the mythos of Charlemagne's Europe. Ogier the Dane wielded the blade Cortana, and after his fight was done, he went into a deep sleep under a castle in Denmark, where he supposedly slumbers to this very day, so he can awaken when Denmark has need of him again.
Who else worked for Charlemagne? Roland, wielder of Durandal. And Charlemagne wielded Joyeuse, and Durandal, Joyeuse, and Cortana were all forged of the same steel.
Yeah. I'm a literature geek because I caught the reference immediately.