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 of the former Anglo-Saxon settlement of Berkhamsted. Subsequent kings granted the castle to their chancellors. The castle was substantially expanded in the mid-12th century, probably by Thomas Becket.
The castle was besieged in 1216 during the civil war between King John and rebellious barons, who were supported by France. It was successfully captured after Prince Louis, the future Louis VIII, attacked it with siege engines for twenty days, forcing the garrison to surrender.