Berkhamsted Castle is a Norman motte-and-bailey castle at Berkhamsted in Hertfordshire, England. The castle was built during the Norman conquest of England in the 11th century to control a key route between London and the Midlands. Robert of Mortain, William the Conqueror's half brother, was probably responsible for the construction and became the subsequent owner of the fortification. A motte and bailey design, the castle was surrounded by extensive protective earthworks and a deer park for hunting. The future town of Berkhamsted grew up alongside it. Subsequent kings granted the castle to their chancellors and it was substantially extended in the mid-12th century, probably by Thomas Becket.