In a later tradition, Lyonesse is identified as a sunken land lying off the Isles of Scilly, to the south-west of Cornwall. 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.
Alfred, Lord Tennyson's Arthurian epic Idylls of the King, describes Lyonesse as the site of the final battle between Arthur and Mordred. One passage in particular references legends of Lyonesse as a land fated to sink beneath the ocean:
A real-life counterpart to Lyonesse is the fishing port of Dunwich.
Deriving from a false etymology of Lyonesse, the 'City of Lions' was said in some later traditions to be the capital of the legendary kingdom, situated on what is today the Seven Stones reef, some eighteen miles west of Land's End and eight miles north-east of the Isles of Scilly.
Felix (Felec) is a character in the late Prose Tristan and even later Italian romances. In the latter stories he is made the father of Meliodas.
Son of Felix in later romances. Marries Isabelle, daughter of King Meirchion of Cornwall.
Son of Meliodias. The famous Tristram of Arthurian legend, he is sent by his maternal uncle, King Mark of Cornwall, to fetch the latter's intended bride Iseult from Ireland. Tristram falls in love with Iseult, but ends up marrying a different woman of the same name, Iseult of the White Hands, whom he does not love. He eventually dies of a broken heart, having been tricked by his jealous wife into thinking his true love had forsaken him.
Son of Tristram. Only appears in the very late Italian I Due Tristani.
Following the Battle of Camlann, supposedly in 537, King Arthur's men flee west across Lyonesse, pursued by Mordred and his men. Arthur's men survive by reaching what are now the Isles of Scilly, but Mordred's men perish in the inundation.
The legend of a sunken kingdom appears in both Cornish and Breton mythology. In Christian times it came 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.
There is a Breton parallel in the tale of the Cité d'Ys, similarly drowned as a result of its debauchery with a single virtuous survivor escaping on a horse, in this case King Gradlon. The Welsh equivalent to Lyonesse and Ker Ys is Cantre'r Gwaelod, a legendary drowned kingdom in Cardigan Bay.
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, archaeological evidence of the forest is visible at very low tides, where petrified tree stumps become visible. The importance of the maintenance of this memory can be seen in that it came to be associated with legendary Brythonic hero Arthur.