Ys

Ys is a legendary Breton city & castle lost to the ocean on the coast of Brittany. It has different spellings as well, such as Is & Ker-Is in Breton, Ville d'Ys in French. It is meant to have been in, or on, the Baie de Douamenez. The city name is translated from Breton to English as 'low city'. Ker in Breton is similar to 'cear' in Welsh, while Ys/Is is related to the Welsh word 'isei', the Scottish Gealib 'iosai' and the Irish 'iseai' (low).
King Gradlon (Gralon in Breton) ruled the city which was built on land reclaimed from the sea. It was rich in commerce and the arts with the palace made of marble, gold and cedar. He built it at the bequest of his daughter Gahut, who loved the sea. A dike was built to stop the city being flooded and a gate was opened at low tide to allow ships to enter. The one key that opened the gate was held by the king.
Gradlon was a pious man, while Gahut who sometimes had the name Ahez in some stories), was a frivolous & unrepentant sinner, and some think was a sorceress. She managed to get the key of the king and opened the gate. They key was made of silver or gold. nobody is certain as to which. It was a mistake, and some attribute it to her being drunk.
The sea inundated the city, killing everyone but the king. A Saint (either St. Gwénnolé or St. Corentin) woke the sleeping king and urged him to flee. The king mounted his horse and took his daughter with him. As the water was about to overtake him, a voice called out: "Throw the demon thou carriest into the sea, if thou dost not desire to perish." Dahut fell from the horse's back, and Gradlon was saved.
Either way she drowned and became a Morgen or Mermaid, and drowns men when she can.

Type

Large city