page 48 of 960 of Sir Thomas Malory: Le Morte Darthur: The Definitive Original Text Edition

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Lady Lyle’s sword can only be removed from the sheath by knight who is worthy. She tried at King Royns court (he’s the guy from Ireland who wanted Arthur to pay tribute) but they all failed. All the knights at Camelot give it a pull, but they all fail, too, even Arthur because he is guilty of incest. This is an important judgment on Arthur’s character.