The Welsh tale Culhwch and Olwen provides the earliest mention of Arthur's sword under the name Caledfwlch. In this narrative, the sword is described as one of the treasures of Britain, so bright that its blade shines with its own light. The Welsh The Dream of Rhonabwy adds further detail: the golden hilt bears a design of two chimeras, and "from the mouths of the two was seen two flames of fire, so dreadful that it was not easy for anyone to look." The Irish cognate Caladbolg ("hard lightning") is the sword of Fergus mac Roich in the Ulster Cycle, suggesting a shared Insular Celtic tradition of a supernaturally powerful sword.

In Geoffrey of Monmouth, the sword is called Caliburnus and is described as having been forged in Avalon. It is one of the finest swords in the world, capable of slicing through any material. Robert de Boron's Merlin (c. 1200) introduces the Sword in the Stone narrative: after Uther Pendragon's death, Merlin causes a sword to appear lodged in an anvil atop a stone, with an inscription declaring that whoever can draw it forth is the rightful king. Young Arthur, then a squire serving his foster brother Sir Kay, draws the sword three times - first merely to provide a replacement weapon for Kay, then to demonstrate his claim publicly. In this tradition, the sword is identified with Caliburn.

The Vulgate Cycle (c. 1215-1235) establishes the version most familiar today: after Arthur breaks Caliburn in battle against King Pellinore, Merlin takes him to a lake. An arm "clothed in white samite, mystic, wonderful" rises from the water holding Excalibur. Arthur rows out and takes the sword, and the Lady of the Lake appears. Malory records Merlin's warning to Arthur: the scabbard is worth ten of the sword, and he must not lose it.

Excalibur's scabbard is arguably more valuable than the blade itself. According to Malory, "the bearer of the scabbard cannot lose blood in battle" - wounds received while wearing it do not bleed at all. This supernatural protection makes Arthur effectively invulnerable. The scabbard is later stolen by Morgan le Fay (Arthur's half-sister), who throws it into a lake. This loss is catastrophic: without the scabbard's protection, Arthur becomes vulnerable, and the event is linked to the eventual fall of Camelot.

Excalibur's powers as described across the sources include blinding brightness when drawn - Malory records that "the blade shined so bright it blinded his enemies" - and supernatural sharpness. Chrétien de Troyes describes it as "the finest sword that there was, which sliced through iron as through wood." Alfred, Lord Tennyson adds the poetic detail of words engraved on opposite sides of the blade: "Take me up" on one side and "Cast me away" on the other, from his Idylls of the King.

The sword's final appearance comes at the end of Arthur's life. After the Battle of Camlann, Arthur instructs Sir Bedivere (or Girflet, in some versions) to throw Excalibur into the lake. Bedivere twice disobeys, unable to part with such a treasure, hiding the sword instead. On the third attempt, he finally obeys. An arm rises from the water, catches the sword by the hilt, brandishes it three times, and draws it under. This act symbolises the end of Arthur's reign and the return of sovereignty to the supernatural realm from which it came.

Archaeological discoveries across Europe demonstrate that swords and other valuable metal objects were sometimes deliberately deposited in rivers, lakes and wetlands during the Bronze Age and later periods. Although interpretations vary between sites, researchers have identified possible ritual offerings, acts of symbolic destruction and other forms of deliberate deposition. These discoveries provide a historical parallel to the Arthurian tradition of Excalibur being returned to the lake.

An archaeological study published in 2018 by Francesco di Gennaro, Silvano Agostini and Vincenzo d'Ercole examined Bronze Age swords recovered across central Italy, including two previously discovered examples from Lake Mezzano. In October 2026, the Italian archaeological authority announced the recovery of a third sword from the same submerged settlement. Dating to the 13th century BCE, the bronze weapon was exceptionally well preserved and retained a cutting edge. Its discovery, together with other bronze objects recovered from the lake, has encouraged further investigation into the practical, social and possible ritual significance of weapons deposited in watery environments.

Comparable discoveries in Britain, including Bronze Age weapons from Duddingston Loch in Scotland, demonstrate that the deposition of swords and other weapons in water was not limited to one geographical region. However, these finds belong to different archaeological contexts, and their purposes cannot always be established with certainty.

The resemblance to Excalibur's return to the lake is particularly striking. In Thomas Malory's "Le Morte d'Arthur", Sir Bedivere casts the sword into the water, where a mysterious hand rises to receive it. Although ancient weapon deposits provide a plausible cultural parallel for this literary motif, no direct historical connection has been demonstrated between any particular archaeological discovery and the development of the Excalibur legend. The archaeological evidence illustrates the antiquity of such practices without establishing that they inspired the medieval Arthurian narrative.