Geoffrey of Monmouth identifies Agned with the Dolorous Mountain, where the Castle of Maidens stood. Geoffrey seems to mean Edinburgh in Scotland, though it is unsure whether Nennius intended this identification. Another theory holds that Agned is a corruption of Andegavum, or Angers in France. A manuscript from the tenth-century give the name Breguion instead, later known as the Castle of Maidens, and has had High Rochester suggested as its actual location.
Historia Brittonum | Probably Nennius, early 9th century
Historia Regum Britanniae | Geoffrey of Monmouth, c. 1138