What is the story of King Arthur's sword Excalibur?

Hello! Literary historian here, specialising in medieval literature. I saw this question after it was cross-posted in r/arthurian.

The earliest surviving account of the legend of Excalibur comes from Geoffrey of Monmouth’s Historia Regum Brittaniae, or History of the Kings of Britain, which was composed c. 1136. Because Geoffrey was writing in Latin, Excalibur’s name is given as Caliburnus (Caliburn in the English translation). Geoffrey claimed to be basing his account of Arthur off of earlier tales/works he heard while growing up in Wales. In early (but not as early as Geoffrey of Monmouth) Welsh legends, the name of the sword is Caledfwlch, which translates to ‘hard-cleaving’.

In this version, Excalibur has nothing to do with Arthur’s right to the throne, proof that he is the one true king. Caliburn is ‘peerless’, best amongst all swords, and it was forged on the Isle of Avalon. He also carries a spear named Ron. Geoffrey of Monmouth gives us several battle scenes in which Arthur fights well while using Caliburn, but there is no pulling of the sword from the stone, receiving it from the Lady of the Lake, returning the sword to the lake as Arthur is dying, or any of the other magical narrative bits we tend to think of when we think of Excalibur.

There are dozens of versions of the Arthurian legend that were written over the course of the medieval era. The Old French Lancelot-Grail (which is made up of two parts, the Vulgate Cycle and Post-Vulgate Cycle) is a particularly famous version. The version which arguably has been the most influential on post-medieval adaptations of the Arthurian legend is Sir Thomas Malory’s Le Morte Darthur, which was written in 1469–1470. It used the Lancelot-Grail as one of its sources, along with several other texts. Two copies of Le Morte Darthur exist, and they have some discrepancies between them: the version published by William Caxton in 1485, and the Winchester manuscript, composed c. 1471–1480. If you want to read Malory’s version of the Arthurian legend, the best scholarly editions are Le Morte Darthuredited by P.J.C. Field that came out in 2013, or the third edition of Malory’s Works, edited by Eugène Vinaver and published in 1990.

In Malory’s version, Arthur has two swords consecutively: the sword in the stone and the sword he receives from the Lady of the Lake. The sword in the stone is not Excalibur.

Uther Pendragon was king of England. He wanted to sleep with Igraine, the wife of Gorlois, the duke of Cornwall. Igraine was faithful to her husband. Uther starts a civil war against Gorlois and Igraine. He kills Gorlois, rapes Igraine (thus conceiving Arthur), and then demands that she marry him. When Arthur is born, Merlin and Uther arrange for him to be immediately smuggled out of the castle and raised as a foster child in the countryside by one of Uther’s loyal knights, Sir Ector. Sir Ector doesn’t know that the baby is the king’s son.

Uther dies, leaving the kingdom without an heir to the throne. A large stone appears as if by miracle in a churchyard in London. It has an anvil stuck on top of it, and a sword rammed through both anvil and stone. The writing on the stone reads (and I’m paraphrasing): ‘Whoever can pull out this sword is the rightful king of England’. Many try, all fail.

Years pass. Sir Ector's biological son Kay is knighted and Arthur acts as his squire. There is a tournament in/near London, and Kay wants to participate. They travel to London. On the day of the tournament, Kay forgets his sword back in the inn. He sends Arthur to go fetch it, the inn door is locked. Arthur remembers seeing a sword stuck in a stone and anvil in a churchyard he passed on his way to the inn. He goes to the churchyard and pulls it out. Sir Ector recognises the sword for what it is and realises that his foster son is Uther's heir.

This sword never gets a name. But it is not Excalibur. At least not in Malory’s version.

After Arthur is crowned, he gets into a one-on-one fight with King Pellinore, and the sword in the stone breaks. Merlin then takes Arthur to the lake of Avalon, where a hand and arm covered in samite cloth rises from the middle of the lake, holding Excalibur, which, Malory tells his audience, means ‘cut-steel’. (Medieval authors loved giving fake etymology for words.) The Lady of the Lake tells Arthur that he can have Excalibur if he promises to grant her an unspecified favour, to be collected at a later date.

Merlin asks Arthur, ‘Which do you like better, the sword or the scabbard?’. Arthur replies that he likes the sword better, because duh, it’s the weapon part. Merlin rebukes him and says the scabbard is worth ten times the sword because it prevents bloodshed. And Excalibur’s sheath is magical: whoever is wearing the scabbard cannot die of blood loss on the battlefield. Arthur promptly gives the sword and scabbard to his half-sister Morgan le Fay for safekeeping. She has a counterfeit made and gives the original sword and scabbard to her lover, Accolon, as part of her scheme to take over the throne.

The Lady of the Lake appears at court some time later and reminds Arthur that he owes her a favour. She wants his best knight’s head. The best knight at that time was Sir Balin – Gawain and Lancelot are children and have not yet been knighted, and Galahad hasn’t even been born. To make a long story short, things do not go to plan and Balin beheads the lady.

Later in the narrative, Malory introduces Nyneve as the new Lady of the Lake. Because of how medieval letters were formed, the spelling of Nyneve’s name is sometimes confused and written wildly differently – Vivian, Nimian, Nimue, and Nyneve are all versions of the same name that, in many medieval handwriting styles, look pretty much the same on the page – just a series of short downstrokes called minims.

Thanks to some of Morgan le Fay’s spells, Arthur ends up in single combat with Morgan’s lover, Accolon. Except Accolon is fighting with the real Excalibur and sheath, which Arthur swiftly realizes when he starts losing a lot of blood on the field. Nyneve sees what’s going on, rides in, and rescues Arthur. She gets Excalibur back to him. Sadly, Morgan manages to abscond with the real scabbard and chucks it into the lake.

Many adventures ensue, but nothing much to do with Excalibur. Cut to the end of the book, when Arthur and his son Mordred have given each other mortal wounds at the battle of Camlann. The dying Arthur instructs his cupbearer, Sir Bedivere, to take him to the shore of the lake of Avalon. He tells Bedivere to throw Excalibur into the lake. Bedivere can’t bring himself to throw away the symbol of Arthur’s kingship, so he hides the sword. Arthur asks Bedivere what he saw when he threw the sword in, and Bedivere replies, ‘Nothing but wind and waves.’ Arthur is angry, knowing Bedivere has lied to him. This happens three times. Finally Bedivere actually throws Excalibur into the lake. An arm, clothed in white samite cloth, reaches up from the middle of the lake, catches the sword, and brandishes it three times (a sort of salute) before disappearing beneath the surface of the water.

At this point in his narrative, Malory gets deliberately hazy and provides his audience with two options. They are invited to choose whichever one they believe the most. Some sources, he says, claim that Arthur died of his wounds shortly thereafter, and his grave can be found at Glastonbury Abbey, near the former lake of Avalon. Other sources claim that after Excalibur was returned to the lake, Nyneve, Morgan, and several other damsels of the lake arrive in a boat and take the dying Arthur off to the isle of Avalon, where he was healed and now sleeps, waiting to be called back to England to aid the kingdom in its hour of need.

In later adaptations of the narrative, the sword in the stone and the sword given by the Lady of the Lake are often conflated, so authors or screenwriters will have Arthur pulling Excalibur out of the stone as a miracle proving his right to the throne, and then returning Excalibur to the lake as he is dying.

Further discussion on Excalibur would be welcome over at r/arthurian!