 The "Mabinogion", translated into English in the mid-nineteenth century by Lady Charlotte Guest, mentions such stones on two occasions.In the story of Peredur son of Efrawg (Percival of the Arthurian cycle), in a departure from Chrétien de Troyes' "Perceval, the Story of the Grail", Peredur is given a magical stone that allows him to see and kill an invisible creature called the Addanc.In another tale, "Owain, or the Lady of the Fountain" (Ywain of Arthurian legend), the hero Owain mab Urien is trapped in the gatehouse of a castle.