In the medieval Arthurian romance The Knight with the Two Swords, also known as The Tale of Balin, Sir Balin recieves the magical sword with two scabbards from a mysterious damsel who comes to Arthur’s court at Camelot.
Her intention is to bestow the sword upon the knight who is deemed the worthiest and most valiant. She carries the swords with two scabbards, one of which renders the wielder invulnerable to all blows, and the other that can cause deadly wounds.
The damsel presents the sword to King Arthur’s court, claiming that only a passing good knight of his hands and deeds, one who was without villainy and of gentle blood on both sides, could pull it out and free her of the encumbrance. This is a classic type of test for knightly virtue; in this case it seems to have been a trap to get Balin le Savage to draw the sword and with it slay the damsel’s brother, who had killed her sweetheart.
The knights engage in a competition to determine who should receive the sword. Eventually, Sir Balin is deemed the worthiest and is granted the magical weapon. The damsel requested it back, saying that if he kept it, it would be the destruction of him and the man he loved most in the world. Unaware of the sword’s dual nature and its potential for tragedy, Sir Balin takes possession of the weapon and sets out on his adventures, unaware of the future challenges it will bring.
The prediction came true when the brothers Balin and Balan, not knowing the other’s identity, gave each other their death wounds in battle.
Merlin put a new pommel on Balin’s sword and put it in a block of floating red marble. He also left the scabbard at the castle where Balin was buried, for Galahad to find. When Galahad arrived in Camelot some years later, he was already wearing the empty scabbard, having apparently picked it up on his way. The sword had just come floating down to Camelot in its block of marble, for the court to marvel at it and read in golden letters on its jewel-decked pommel:
Never shall man take me hence, but only he by whose side I ought to hang, and he shall be the best knight of the world.
Lancelot had refused to make the attempt, remarking that whoever tried and failed would recieve a grievous wound of that sword. At Arthur’s urging, Gawaine reluctantly made the attempt, for which, sure enough, the sword later wounded him. Percivale also made the attempt, but, being almost as pure as Galahad, suffered no retribution from this sword. (However, he did wound himself in the thigh with his own sword in self-penance for having almost been seduced by the fiend.) Galahad, of course, drew the sword.
Merlin had also predicted that with Balin’s Sword Lancelot would slay the man whom he loved best, which was Gawaine. Either there is a confusion here between Lancelot and his son – for it is Galahad who deals Gawaine a grievous, not a mortal, wound with Balin’s Sword – or else Galahad sent the sword back by Sir Bors to his father Lancelot, who later used it in the fatal combat with Gawaine.