Fictional elements introduced in the 11th century

Excalibur is the mythical sword of King Arthur that may possess magical powers or be associated with the rightful sovereignty of Britain. Its first reliably datable appearance is found in Geoffrey of Monmouth's Historia Regum Britanniae. Excalibur as the "sword in the stone" functioning as the proof of Arthur's lineage is an iconic motif featured throughout most works dealing with Arthur's youth since its introduction in Robert de Boron's Merlin. The sword given to the young Arthur by the Lady of the Lake in the tradition that began soon afterwards with the Post-Vulgate Cycle is not the same weapon, but in Le Morte d'Arthur both of them share the name of Excalibur. Several similar swords and other weapons also appear within Arthurian texts, as well as in other legends.