Apparently this was in the vicinity of the Dolorous Tower, for the Lady of Briestoc lost all her knights while attempting to rescue Gawaine from Carados. It is possible that Briestoc could be counted as a subkingdom, but one can more easily imagine Carados destroying the force of a single castle than that of an entire subkingdom.
If Turquine’s Hill is accepted as Cadbury, and Carados’ Dolorous Tower put somewhere in the middle of modern Devonshire, the Briestoc might be identified with Botreaux. On the other hand, if Botreaux were Briestoc, the lady would have had troublesome neighbors at Tintagil – first the giants and later King Mark – too close for her to be that concerned about Carados farther away. Almost due south of Tintagil, about eight miles from the tip of the southern coast of Cornwall, is Brodock, or Brotheck. Norden lists it only as a parish, but the name is at least as close as “Botreaux” to “Briestoc”.
Giants of Tintagel | The Legend of King Arthur