Wallingford Castle passed from Robert to first his son-in-law Miles Crispin, and then Brien FitzCount, who married Robert's daughter after Miles died. Brien, an important supporter of Henry I, was the son of the Duke of Brittany, and probably strengthened the castle in stone in the 1130s. He produced a very powerful fortification, including a shell keep and a curtain wall around the bailey, that, combined with the extensive earthworks, has been described by historian Nicholas Brooks as "one of the most powerful royal castles of the 12th and 13th centuries".