What do we know about the Sword Excalibur?

Geoffrey of Monmouth, Wace, and Layamon all observe that Arthur's sword Caliburn was forged on the Isle of Avalon. In Sir Thomas Malory's Morte d’ Arthur, Excalibur is the name given to the sword Arthur receives from the Lady of the Lake and entrusts to Bedivere to return to the water after his final battle. Malory, following his French source, explains the name Excalibur as meaning 'Kutte [Cut] Steele’. (There is only one place in the Morte where the sword drawn from the stone is referred to as Excalibur: in his battle with the kings who will not accept him, Arthur pulls the sword from the stone, on Merlin's advice, only when he is losing the battle. When he draws ‘his swerd Excalibur’, it gives the light of thirty torches and helps him to put his enemies to flight.) When this sword from the stone breaks in two as Arthur fights Pellinore, Merlin saves Arthur by casting an enchantment over Pellinore and then takes the king to receive another sword, Excalibur, from the Lady of the Lake. Merlin tells Arthur that Excalibur's scabbard is even more valuable than the sword itself because while he wears it he will not lose any blood or be severely wounded. Morgan le Fay, to whom Arthur has entrusted the care of Excalibur. gives the sword to her lover Accolon to use against Arthur. Provided with a counterfeit Excalibur, ‘Arthur is saved by Nyneve (a character sometimes called Vivien, Niniane, or Nimue). Morgan then steals the scabbard and throws it into a lake so it can no longer protect Arthur. Excalibur must be returned to the water at the end of Arthur's life, a task assigned to Bedivere in Malory's account, but to others in different medieval versions of Arthur's story.