But fierce Pyrrochles, lacking his owne sword,
  The want thereof now greatly gan to plaine,
  And Archimage besought, him that afford,
  Which he had brought for Braggadocchio vaine.
  So would I (said th'enchaunter) glad and faine
  Beteeme to you this sword, you to defend,
  Or ought that else your honour might maintaine,
  But that this weapons powre I well haue kend,
To be contrarie to the worke, which ye intend.

For that same knights owne sword this is of yore,
  Which Merlin made by his almightie art
  For that his noursling, when he knighthood swore,
  Therewith to doen his foes eternall smart.
  The metall first he mixt with Medæwart,
  That no enchauntment from his dint might saue;
  That it in flames of Aetna wrought apart,
  And seuen times dipped in the bitter waue
Of hellish Styx, which hidden vertue to it gaue.

The vertue is, that neither steele, nor stone
  The stroke thereof from entrance may defend;
  Ne euer may be vsed by his fone,
  Ne forst his rightfull owner to offend,
  Ne euer will it breake, ne euer bend.
  Wherefore Morddure it rightfully is hight.

The Faerie Queene, Book II, Canto VIII