Christchurch in Dorset is centred on a slightly raised triangle of land at the confluence of the Avon and Stour rivers, surrounded by water on three sides and so easily defensible, and overlooking the important anchorage of Christchurch Harbour just downstream. The town was founded by The Saxons in the 7th century and its strategic importance was recognised by the Normans, who built a motte and bailey fort soon after the 1066 conquest, replaced with a stone keep in the 12th century. This was enclosed by a moat, as was the outer bailey, a walled area containing various subsidiary buildings, the largest a fine two-storey house.
The moat has long since been filled in, and the castle keep was greatly damaged after the Civil War; only two of its four walls remain, but the house also survives relatively intact, and represents a very rare example of a residence from the early Norman period. The two buildings fall within a sizeable historic district that also includes the 12th century Christchurch Priory, the longest parish church in England. The castle partly overlooks the rear of two rows of shops, which detract somewhat from its historic ambience, yet the site as a whole is still impressive, one of the highlights of the town, even though all can be seen in just a short time. Both buildings are managed by English Heritage, are free to enter, and open all year.
The first fortification at Christchurch (at that time known as Twynham, meaning 'place between the rivers') was a small wooden structure constructed in the early 10th century; the Normans added a ditch around the perimeter, and a fortified bailey on the east side, enclosed by a wooden fence. The construction was probably overseen by Richard de Redvers (died 1107), one of the companions of William the Conqueror. The masonry keep was erected around 1150, and subsequently enlarged; it was linked to the bailey, by now also walled with stone, via a bridge over the moat. The keep had two main floors above a basement, which stood above ground level when built, but was then surrounded with earth, creating a defensive mound. The castle passed to the Crown in 1293 and remained relatively unchanged for several centuries, used for residential purposes, until the Civil War, after which, following a unsuccessful attempt at capture by Royalists, it was slighted by order of Oliver Cromwell, to prevent any further military use. The moat was filled in, and all the buildings in the bailey were dismantled, apart from the main house. Much of the stonework was reused by the local townspeople.
Christchurch Castle lies on the south side of Castle Street, close to the River Avon, adjoining another drainage (Mill Stream), which was excavated in the 13th century to provide sanitation - this runs right alongside the Norman house, and also formed part of the castle defences. The rest of the bailey is now occupied by a bowling green, and there is no sign of the moat that once encircled the castle. The ruins of the keep stand on top of the still steep-sided mound, or motte, reached by two flights of steps that meet in the floor of the tower. This was approximately square in cross section, about 50 feet across, with chamfered corners, and two of its walls survive, to the east and west; the former includes two windows and a smaller opening that once led to the basement, while the latter has just one window. The first floor level is evident from a few corbels, but apart from these there are no other obvious architectural details.
The Norman house, also known as the constable's house, is 280 feet northeast of the keep; a two-storey rectangular building that contained one room on each floor (though probably partitioned with wooden screens), below a gable roof, plus a small garderobe turret at the southeast corner. The ground floor was a basement, and above was a great hall and bedchamber; the upper walls contain several two-light windows, with decorative round heads, and a fireplace, all still relatively complete, while above, near the centre of the east wall, is a tall, round chimney, one of only five in the country to survive from this period. The top floor was accessed by a narrow spiral staircase, at the northeast corner; most of the steps are still visible.