title: Excalibur
context: 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).[3][4][1] 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.[5]
question: When did the legend of the Excalibur sword originate?
answers: 1136