From A Gazetteer of Arthurian Topographic Folklore:
Ashe [quoted in Grooms, 1993, p.115] writes that ‘Legend has it that when Arthur was walking through Carmarthenshire on his way to Camlann, he felt a pebble in his shoe and tossed it away. It flew seven miles over Burry Inlet and landed in Gower, on top of the smaller stones of Maen Cetti.‘