Alexanderstone Castle is an early 12th century earthwork motte and bailey fortress, founded by the Mora family. The sub-oval motte, with the remains of its encasing ditch on the east side, is also crowned by an eastern rampart. The small semi-circular bailey which is scarped to north-west, has been damaged by ploughing but it still retains traces of its rampart and ditch. The farmhouse which possibly stands in another bailey, cuts into the south-east side of a motte. To the south-west is Troed-yr-harn Motte Brecon, a possible 13th century siege-castle and 2 miles north-west is Llanddew Bishop's Palace.