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.
Chronology of bladed weapons
The first bronze swords with a length equal to or greater than 60 cm date from the 17th century BC in regions of the Black Sea and the Aegean Sea. They emerged as an evolution of shorter weapons of the type of the daggers or daggers. To make a sword useful in combat, you must have a correct alloy, give it the right shape and apply the necessary thermal (and finishing) treatments. The longer a sword, the stresses (bending and buckling) are more important. What is needed is a weapon that is hard enough (to cut), fairly flexible (without being fragile) and quite tenacious enough to withstand the blows in the fights.