Lyonesse is a country in Arthurian legend, particularly in
the story of Tristan and Iseult. Said to border Cornwall, it is most notable as
the home of the hero Tristan, whose father was king. In later traditions
Lyonesse is said to have sunk beneath the waves some time after the Tristan
stories take place, making it similar to Ys and other lost lands in medieval
Celtic tales, and perhaps connecting it with the Isles of Scilly.
In medieval Arthurian legend, there are no references to the
sinking of Lyonesse, for the simple reason that the name originally referred to
a still-existing place. Lyonesse is an English alteration of French Léoneis or
Léonois (earlier Loönois), a development of Lodonesia, the Latin name for
Lothian in Scotland. Continental writers of Arthurian romances were often
puzzled by the internal geography of Great Britain; thus it is that the author
French Prose Tristan appears to place Léonois contiguous, by land, to Cornwall.
In English adaptations of the French tales, Léonois, now "Lyonesse",
becomes a kingdom wholly distinct from Lothian, and closely associated with the
Cornish region, though its exact geographical location remained unspecified.
The name was not attached to Cornish legends of lost coastal lands until the
reign of Elizabeth I of England, however. However, the legendary lost land
between Land's End and Scilly has a distinct Cornish name: Lethowsow. This
derives from the Cornish name for the Seven Stones reef, on the reputed site of
the lost land's capital and the site of the notorious wreck of the Torrey
Canyon. The name translates into English as "the milky ones", from
the constant white water surrounding the reef.