The Breton lays that we have from the twelfth and thirteenth centuries, on the evidence of the opening passages in "Tyolet" and others, describing their transmission, are possibly derived from stories that are considerably older, although the desire of medieval authors to "seek to ensure a measure of authenticity for their tales" should be remembered. Similarities in "Tyolet" and the Second Continuation of Chrétien's "Perceval, le Conte du Graal" has led R. H. Loomis to observe that the two stories "must derive from a common remote source".