This paper studies the literary origin of the Grail legend in medieval French literature, taking into account two important romances: Le Conte du Graal by Chrétien de Troyes and Le Roman de l’Estoire dou Graal by Robert de Boron. In these two texts the authors established the basis for the development of a new subject matter around the mysterious object called “Grail” from the Middle Ages to the present times. It will also be shown how an object, not totally sacred in Chrétien de Troyes, becomes a relic related with Jesus’s blood in Robert de Boron.