Des Mares, Marasse
The castle Des Mares would probably be near the sea (mare).
The castellan, Agravadain des Vaus des Galoire (not to be confused with Gawaine’s brother, Agravaine), had a beautiful daughter whom Merlin admired and caused to sleep with Ban, resulting in the birth of Lancelot’s half-brother, Ector de Maris.
Kings Ban and Bors stopped here during their visit to Arthur in Britain, and Hector (Ector de Maris) stays here before reaching Gazewilte.
See also
Damsel des Mares | The Legend of King Arthur