Chastel des Quatre Pierres
Sir Balan visited this castle, where he heard news of his brother Balin. It was in Bagdemagus’s kingdom. Perhaps it was somewhere mountainous, or near a dolmen or cromlech, and hence got its name.
According to Vulgate, Meliagrant’s body, after Lancelot killed him, was taken to the Castle of Four Stones. From this it would appear that Four Stones was either Meliagrant’s own castle, or the castle of a friend.
Sources
Vulgate Lancelot | 1215-1230
Post-Vulgate Mort Artu | 1230-1240
Le Morte Darthur | Sir Thomas Malory, 1469-1470