certain properties of the sword of light (such as screaming when touched in order to alert its owner) is likely borrowed from Arthurian material, because there is evidence that a version of Fios Fatha an Aonsceil ('the knowledge of the cause of the One Story') had been told about Gearóid Iarla (Earl Gerald FitzGerald) of the 14th century, whose family had close ties with Arthurian tradition. To the Earl is attached a Barbarossa legend (King asleep in mountain motif), which makes the figure conducive to be transformed into a "sleeping giant" of folktale. Grail sword Other commentators have equated the Sword of Light to the Grail sword. Loomis also suggested that the sword obtained by Cei (Sir Kay) in the Welsh tale Culhwch and Olwen (i.e., the sword of Gwrnach the giant) must be "related to the sword of light which is the object of the Irish and Scottish folk-tales". See also Lugh's spear Lúin of Celtchar Irish mythology in popular culture Four Treasures of the Tuatha Dé Danann Nuada Airgetlám Explanatory notes References Citations Bibliography Irish or Scottish Gaelic texts, some with translations Vol. I II) Translations or tales collected in English ; text via Internet Archive Critical studies Popularized versions , a composite retelling. External links Celtic Objects Encyclopaedia of the Celts Mythological cycle Ulster Cycle Mythological swords