Excalibur
Geoffrey of Monmouth, in his "Historia Regum Britanniae" ("The History of the Kings of Britain", c. 1136), Latinised the name of Arthur's sword as "Caliburnus" (potentially influenced by the Medieval Latin spelling "calibs" of Classical Latin "chalybs", from Greek "chályps" ["χάλυψ"] "steel"). Most Celticists consider Geoffrey's "Caliburnus" to be derivative of a lost Old Welsh text in which "bwlch" (Old Welsh "bulc[h]") had not yet been lenited to "fwlch" (Middle Welsh "vwlch" or "uwlch"). In the late 15th/early 16th-century Middle Cornish play "Beunans Ke", Arthur's sword is called "Calesvol", which is etymologically an exact Middle Cornish cognate of the Welsh "Caledfwlch". It is unclear if the name was borrowed from the Welsh (if so, it must have been an early loan, for phonological reasons), or represents an early, pan-Brittonic traditional name for Arthur's sword.
Wace
"Roman de Brut" (c. 1155) was based on the "Historia Regum Britanniae" of Geoffrey of Monmouth. It cannot be regarded as a history in any modern sense, although Wace often distinguishes between what he knows and what he does not know, or has been unable to find out. Wace narrates the founding of Britain by Brutus of Troy to the end of the legendary British history created by Geoffrey of Monmouth. The popularity of this work is explained by the new accessibility to a wider public of the Arthur legend in a vernacular language. In the midst of the Arthurian section of the text, Wace was the first to mention the legend of King Arthur's Round Table and the first to ascribe the name Excalibur to Arthur's sword, although on the whole he adds only minor details to Geoffrey's text.