Three entries with the name Maine.
Maines, Mainet, Meines, Mene, Moine, Moyne
In the Vulgate Merlin, Arthur’s great uncle, apparently the oldest, of King Constans of England, Arthur’s grandfather, who preceded Vortigern as King of Britain. He is called Constans in the chronicles.
The son of Constantine and Ivoire, and brother of Uther and Pendragon, Maine was foisted to the throne by Vortigern after his father’s death. He was an impotent king, and Vortigern eventually had him assassinated, killed by a dozen barons who wanted Vortigern for their king. Maine survived and was avenged by his brothers.
The alternate name for Constans undoubtedly comes from his title in the chronicles: le Moine, or “the Monk.”
Vulgate Merlin | 1220-1235
Unknown (the pre-Arthurian period) | Baudin Butor, c. 1290
Arthour and Merlin | Late 13th century
Historia Regum Britanniae | Geoffrey of Monmouth, c. 1138
Arthur and the King fought a battle near the river.
Matrona | The Legend of King Arthur
Lancelot do Lac | 1215-1220