Before the Norman Conquest there were no masonry built castles in Cornwall, only stockades of wood surmounting earthworks or piled up masses of stone uncemented. The usual Saxon _Burh_ was a mound, surmounted by a structure of timber, reached by a bridge or ladder from a base-court that was encompassed by moat and mound and stockade. The Norman system of building a castle was to erect a round or square keep, a massive structure of stone, on the mound that had formerly been surmounted by a wooden structure, and to surround the base-court with a stone wall. Within this were erected the necessary domestic buildings. Very generally the entrance to the court was strongly defended by a second tower. The style of castle was greatly altered in the reign of Edward I but of such Edwardian castles there are no examples in Cornwall, save the poor fragment of Tintagel. The Normans built a castle at Launceston, and there the circular keep standing on a lofty tump of rock, artificially shaped, is of their construction, but the ruined buildings below, with the gateways and walls of the base-court, are later. The castle of Trematon also consists of a "motte" surmounted by a circular keep, and a base-court with square tower at the entrance, with an archway. Tintagel Castle is reduced to a miserable ruin, part on the mainland, part on the islet, with the intervening portion blocked up by fallen rocks, forming a narrow isthmus. The deep chasm that formerly separated the two portions of the castle was anciently spanned by a drawbridge. The work appears to be of the thirteenth century. On the island are the remains of a chapel with its altar slab still in place. Tintagel became a residence of the Earls of Cornwall, and in 1245, Richard son of King John received in it his nephew David, Prince of Wales. It was subsequently used occasionally as a prison. In the reign of Elizabeth, that penurious queen, deeming the expense of keeping it up too onerous, allowed it to fall into ruin. St Michael's Mount was crowned with a castle and a church. The oldest portion is the central tower, of the fourteenth or fifteenth century; other portions are later additions, and much very bad modern work has tended to its sad disfigurement. Edward the Confessor planted a monastery on the rock, and granted it to Mont S. Michel in Normandy; at the Conquest it was made over to Robert Earl of Mortain, but the Benedictines of Mont S. Michel continued to have a cell there with a prior. It was consequently at once a religious house and a military post.