Deal Castle, a Henrician artillery castle, was built in 1539 by Henry VIII as part of his chain of coastal defences in response to the growing threat of invasion at that time. The castle, which was designed to resemble a Tudor rose, was built, along with Sandown and Walmer Castles, to protect the good landing grounds and strategic anchorage between the Goodwin Sands and the coast; an area known as the Downs. A series of bulwarks, or earthen defences, were also built along the coast between the three castles.
The castle did not however see any action until the Civil War when it was captured during the Royalist revolt in Kent in 1648 and held for several weeks. The castle's defences continued to be maintained and repaired during the 18th and 19th centuries. However, the changes reflected a general change in its function from that of a decreasing military role to one of a more residential nature. The castle became the residence for the honorary post of Captain of the Cinque Ports. In 1951 the castle was taken over by the Ministry of Public Building and Works and it continues to be part of the Crown Estate and is now run by English Heritage.
Deal castle is built of Kentish ragstone, brick, and Caen stone reused from nearby dissolved religious houses. The castle has a circular, symmetrical plan and originally had 145 gun-ports on five tiers. At the centre of the castle is a three-storeyed circular tower, with six semicircular, slightly lower towers projecting from its external face. This is surrounded by a curtain wall with six low semicircular bastions with gun platforms on their upper levels for heavy guns. There was a continuous gallery known as the rounds at the basement level of the bastions that had 53 hand gun-ports to provide flanking fire of the bottom of the moat. The castle buildings are further protected by a stone-lined dry moat and a gatehouse. The gatehouse was equipped with a number of defensive features including murder holes and a gun-port.