I imagine Cost and the difficulty/skill of forging a decent Sword would be a big part of a Sword's Mythos.
To please their personal God/ask for a favour, perhaps before a Battle, Ancient Britons/Celts would throw their most valuable and important possession, their personal Sword into lakes/rivers, and in those days, only a King, Chieftain or Warlord would even be able to afford a Sword, with most Warriors having to make do with Spears.
It is probably why the "Lady in the Lake" entered Arthurian mythology when the Normans & the Church began hijacking the Welsh Legends for propaganda purposes in medieval times - a part remembered Briton tradition of throwing Swords into a body of water, every river, lake etc would have had a personal God or Goddess attached to it, so it makes sense that such an activity is behind the Lady.
Equally, the Sword in the Stone origin of Caledfwlch/Caliburn/Excalibur may relate to how Swords were forged in ancient Britain, using a stone mold. I have read an intriguing second possibility a Historian came up with for Arthur's Sword in the Stone though - Modern Welsh, Old Welsh/late Brythonic have a good few Latin words - Welsh words like Caer (fortified place), Ffenestri (Window) and Dydd Llun (Monday) are all Latin based words that entered the language.
A lot of people think that Arthur was definately a real figure, he just was not a King, as the Welsh/British Royal genealogies of the dark age kingdoms are well recorded, and there is no King Arthur at the right time, but the name does suddenly gain some popularity, as if little Princes were being named for a great Hero. The chap pointed out that Latin for Stone in some uses was "Saxum" which of course sounds similar to Saxon, the Welsh Arthurian Myths were generally recorded by Scholars in Latin - and it is entirely possible that what the Stories are partially but incorrectly recording/remembering is not that Arthur pulled a Sword from a Stone, thus proving his right to a Throne, but that Arthur perhaps during a battle, had a personal Combat with a mighty Saxon King or Chieftain, and defeated him, thus taking the Saxon's Sword as the spoils of war, possibly even taking the sword from the Saxon, and finishing him off with it - thus what he actually did was "take the Sword from the Saxon" but an inattentive scholar got Saxon and Saxum mixed up.
In the Dark Ages too, Swords and Armour dating back to the Roman, and pretty much irreplaceable, with the knowledge of how to forge such things having died out, along with the knowledge and skills to build and maintain the Roads, Palaces, Villas and towns the Romans built, things like weapons and armour would have been jealously hoarded, and passed down from Father to Son, so another fetishisation of warrior items, helping the Sword become a noble weapon.
