Excalibur is the sword of the king arthur melagenda. There are two swords which appeared in legends arthur: Sword in the stone, which can only be revoked by arthur, thus proving a legitimate kingdom, and a sword given to him by the lady of the lake.
In some versions there is only one sword, while in another version, the sword in the stone and then broken and then Arthur receives Excalibur from the Lady of the lake. The origins of magic sword that can not be solved until now