Lyonesse, Lyoness, or Lyonnesse is the lost sunken land believed in legend to lie off the Isles of Scilly, to the south-west of Cornwall. It is sometimes associated with Avalon. The Trevelyan family of Cornwall takes its coat of arms from a local legend; 'when Lyonesse sank beneath the waves only a man named Trevelyan escaped by riding a white horse.' To this day the family's shield bears a white horse rising from the waves.
Lyonesse in Arthurian legend
According to Arthurian legend, Lyonesse is the birthplace of Tristan, son of King Meliodas (or Rivalen). One of the signs of King Arthur's return will be that Lyonesse will rise from the depths again. Alfred, Lord Tennyson's Arthurian epic, Idylls of the King, describes Lyonesse as the site of the final battle between Arthur and Mordred. A real-life counterpart to Lyonesse is alleged to be the fishing port of Dunwich.
There is evidence that in Roman times the Isles of Scilly comprised one large island, known as Siluram Insulam (or Sylina Insula). According to legend, Lyonesse stretched from Scilly to Land's End at the westernmost tip of Cornwall, and once had some 140 churches. Its capital was the City of Lions (sometimes given as Carlyon), located on what is now the treacherous Seven Stones reef. The names of the kings of Lyonesse are derived from Welsh and Arthurian myth. Following the Battle of Camlann in 537, Arthur's men fled west across Lyonesse, pursued by Mordred and his men. Arthur's men survived by reaching what are now the Isles of Scilly, but Mordred's men perished in the inundation.
Lyonesse in Celtic mythology
Lyonesse was central to both Cornish and Breton mythology. In Christian times it became to be viewed as a sort of Cornish Sodom and Gomorrah, an example of divine wrath provoked by unvirtuous living, although the parallels were limited in that Lyonesse remained in Cornish thought very much a mystical and mythical land, comparable to the role of Tir na nÓg in Irish mythology.
It is often suggested that the tale of Lyonesse represents an extraordinary survival of folk memory of the flooding of the Isles of Scilly and Mount's Bay near Penzance. For example, the Cornish name of St Michael's Mount is Carrack Looz en Cooz - literally, 'the grey rock in the wood'. Cornish people around Penzance still believe strongly in a sunken forest in Mount's Bay, and visitors to the area can be shown 'evidence' of the forest (usually petrified drift wood) by locals. The importance of the maintenance of this memory can be seen in that it came to be associated with legendary Celtic hero Arthur.
Lyonesse in modern fiction
It has been appropriated outside Cornwall as the setting for modern fantasy stories, notably Jack Vance's Lyonesse trilogy. In Stephen R. Lawhead's Pendragon Cycle, Lyonesse is where refugees from Atlantis (the 'Fair Folk') settle, the word Lyonesse being derived from the Celtic corruption of the word Atlantis.
J. R. R. Tolkien drew some of his inspiration for the lost kingdom of Númenor from the legends of Lyonesse; one of the kingdom's many names in his mythos is 'Westernesse'. In Joseph Bédier's Tristan et iseult, Tristan was born in Lyonesse to their king and the princess of Cornwall.