The sword that had belonged to Balin the Savage. It appears in several texts, but is not named in all of them. Balin had received it from a servant of the Lady of the Island of Avalon, and he used it to behead the Lady of the Lake. The Lady of Avalon’s messenger told Balin that the sword would bring him sorrow. Later, he used it to kill his brother Balan, receiving a mortal wound himself in the process. This episode occurred on Merlin’s Island. Merlin took the sword and thrust it into a block of marble.
Gawain saw the sword on the island and was told by a hermit that the weapon, in the hand of his best friend, would cause his death, through the fault of Mordred. Evidently, the hermit was referring to Gawain’s battle with Lancelot, but if Lancelot ever received the sword, we are not told. Instead, the block of marble floated up to Camelot at the beginning of the Grail Quest. Gawain tried to draw it from the stone, failed, and was informed that he would suffer for having tried.
Galahad drew the sword, girded it upon himself, and apparently kept it until he received the Sword of the Strange Hangings. (Possibly, he gave the Adventurous Sword to Lancelot, his father, after receiving the latter.) Fulfilling the second prophecy against Gawain, Galahad struck Gawain down with the sword during the Grail Quest, putting Gawain out of commission for the rest of the adventure.