In the Vulgate Merlin, Arthur comes to possess Marmiadoise (Marmyadose), the Sword of Hercules, forged by Vulcan and passed from heir to heir until it was owned by Rions (Ryons), Arthurís enemy.

The conception of Hercules (or, more properly, Heracles) in Greek mythology precedes that of Arthur: Zeus visited the lady Alcmene in the form of her husband, Amphitryon, much as Uther Pendragon seduced Igerne (Igraine) in the form of her husband, Gorlois.