The Castles is a late 11th century earthwork motte and bailey fortress, founded by Drogo de la Beuvriere. The large flat-topped motte and a series of enclosures that includes baileys and stock-pens, were sub-divided by a complex water-management system. In the wide moat that encases the motte is a northern earthen bank, originally it supported the wooden bridge that gave access to a rectangular bailey. A second triangular bailey, encased by a wide moat, with a rampart on its inner side, lies to the south-east. The tidal Beck which flows into the River Humber, filled the moats and also provided defence for the south side, where the earthworks are not so strong. The site commanded the Humber ferry landfall and possibly replaced a Saxon manor of Earl Morcar. In 1087 the lands passed to Odo of Champagne and a charter of 1189 lists the castle as belonging to Thornton Abbey. Excavations in 1964 found timber foundations and pottery dating from the 11th to 14th century.