In Deheubarth that now South-wales is hight,
  What time king Ryence raign'd, and dealed right,
  The great Magitian Merlin had deuiz'd,
  By his deepe science, and hell-dreaded might,
  A looking glasse, right wondrously aguiz'd,
Whose vertues through the wyde world soone were solemniz'd.

It vertue had, to shew in perfect sight,
  What euer thing was in the world contaynd,
  Betwixt the lowest earth and heauens hight,
  So that it to the looker appertaynd;
  What euer foe had wrought, or frend had faynd,
  Therein discouered was, ne ought mote pas,
  Ne ought in secret from the same remaynd;
  For thy it round and hollow shaped was,
Like to the world it selfe, and seem'd a world of glas.

The Faerie Queene, Book III, Canto II