Vandalior, Vandeberes en Cornoaille, Vandelers
A castle in Cornwall.
According to Malory the rebel kings had to leave off warring with Arthur because the Saracens were besieging their castle of Wandesborow. In the Vulgate, however, the rebel kings were called away from their war with Arthur because the Sesnes, or Saxons, were attacking Vandaliors, in Cornwall (Cornuaille), in the early days of Arthur's reign.
Vandaliors sounds as if it could be a variant of Wandesborow, which see, and Malory might have confused the Sesnes with the Saracens in this passage. Nevertheless, one could consider Wandesborow and Vandaliors as two separate strongholds. Vandaliors I would put on Mount's Bay, Cornwall, either at Penzance or at the Lizard Head. Since Penzance had not in earlier times the prominence it enjoys today, Lizard Head might be better. Just a little north of Lizard Head up the west coast is Goon-goofe, of which Norden tells us:
A mountayne by the sea side ... [its name] signifying the hill of bloude. There are auntiente markes of martiall actes, as trenches of Defence, and hills of Burialls.