The former Saxon fortification known as Twyneham was renamed Christchurch in 1177. The name was taken from a monastery founded in the area by Edward the Confessor in 1043. The first Christchurch Castle was a wooden motte and bailey device put up soon after the Norman Conquest by Richard de Redvers, a Norman baron. It was rebuilt in stone around 1160, during which time a domestic dwelling block was added. Later known as the Norman House, it was used mainly as a residence for the constable, who was responsible for security of the castle complex.

The castle passed to the Crown in 1293. During the English Civil War Parliamentarian troops attacked and seized Christchurch, a Royalist town. In 1645, a Royalist counter-offensive forced the 1,000-strong Parliamentarian army to take refuge in the castle, which they successfully held. At the end of hostilities the castle was slighted and little remained by the end of the 17th century. Today, only parts of the Great Tower and the Constable’s House survive.