What was Excalibur?

“Excalibur, or Caliburn, is the legendary sword of King Arthur, sometimes also attributed with magical powers or associated with the rightful sovereignty of Great Britain. Sometimes Excalibur and the Sword in the Stone (the proof of Arthur’s lineage) are said to be the same weapon, but in most versions, they are considered separate. Excalibur was associated with the Arthurian legend very early. In Welsh, it is called Caledfwlch; in Cornish, Calesvol; in Breton, Kaledvoulc’h; and in Latin, Caliburnus.

In Arthurian romance, a number of explanations are given for Arthur’s possession of Excalibur. In Robert de Boron’s Merlin, the first tale to mention the “sword in the stone” motif, Arthur obtained the British throne by pulling a sword from an anvil sitting atop a stone that appeared in a churchyard on Christmas Eve. In this account, the act could not be performed except by “the true king,” meaning the divinely appointed king or true heir of Uther Pendragon. As Malory’s writes: “Whoso pulleth out this sword of this stone and anvil, is rightwise king born.” This sword is thought by many to be the famous Excalibur, and its identity is made explicit in the later Prose Merlin, part of the Lancelot-Grail cycle. The challenge of drawing a sword from a stone also appears in the Arthurian legends of Galahad, whose achievement of the task indicates that he is destined to find the Holy Grail.” https://en.wikipedia.org/wiki/Excalibur