 Berkhamsted Castle is a Norman motte @-@ and @-@ bailey castle in Berkhamsted , Hertfordshire . The castle was built to obtain control of a key route between London and the Midlands during the Norman conquest of England in the 11th century . Robert of Mortain , William the Conqueror 's half brother , was probably responsible for managing its construction , after which he became the castle 's owner . The castle was surrounded by protective earthworks and a deer park for hunting . The castle became a new administrative centre , and the former Anglo @-@ Saxon settlement of Berkhamsted reorganised around it . Subsequent kings granted the castle to their chancellors . The castle was substantially expanded in the mid @-@ 12th century , probably by Thomas Becket . 
