Illustration from David Aubert's, Chroniques et conquestes de Charlemagne based on Girart de Vienne, a late twelfth-century Old French chanson de geste by Bertrand de Bar-sur-Aube. The work tells the story of the sons of Garin de Monglane and their battles with the Emperor Charlemagne and it establishes the friendship of the epic heroes Oliver and Roland. Olivier is pitted against the nephew of the Emperor, Roland, in a duel near Vienne, but neither hero prevails and, when night comes, an angel tells the two heroes to save their strength for battling infidels. The two swear each other eternal friendship and Roland proposes to Olivier's sister, Aude. Roland (died 778) was a Frankish military leader under Charlemagne who became one of the principal figures in the literary cycle known as the Matter of France. Roland was military governor of the Breton March, with responsibility for defending the frontier of Francia against the Bretons. Oliver was a fictional knight who plays the role of Roland's closest friend, advisor, and confidant, one of Charlemagne's twelve peers and brother of Aude, Roland's betrothed.