Wraiths, creatures of magic, are created using necromancy to reanimate a corpse and cannot be slain by normal weapons, since one cannot simply kill that which is already dead. Both mortal weapons and spells are useless against wraiths. Only a enchantedsword, such as Excalibur, a "sword begotten in the dragon's breath", can destroy them. It is said that wraiths disappear when their task is completed. A Wraith can only be created by using magic to harness the grief and rage of a tormented soul and return it to its corpse, now an indestructible body.
The knight Tristan de Bois, slain in a duel with Uther, was reanimated by Nimueh. Seeking revenge on the king, he killed two Knights of Camelot in combat but he was finally destroyed when struck by Excalibur in his second duel against Uther (Excalibur). This sword was marked to be the only way to defeat the Wraith in the first place, since other magic used by Merlin had no effect on it.