Walmer Castle, a Henrician artillery castle, was built in 1539 by Henry VIII as part of his chain of coastal defences in response to the threat of invasion from Catholic forces. The castle was built along with Sandown and Deal Castles to protect the good landing grounds and strategic anchorage between the Goodwin Sands and the coast, known as the Downs. In 1648, during the Civil War, the castle was captured by Royalists and held for a number of weeks. A number of repairs and alterations have been carried out on the castle. In circa 1730 the castle was enlarged and converted into the official residence of the Lord Warden of the Cinque Ports. Important alterations were carried out in 1874 and during the Second World War a pill box was established there.
Walmer castle consisted of a three-storey circular tower surrounded by four low semicircular bastions connected by a curtain wall. These had gun-platforms on their upper levels to support heavy guns. Contemporary illustrations show that the central tower and bastions were originally capped by broad rounded parapets pierced by gun embrasures. The castle buildings were also protected by a stone-lined dry moat and there was a gatehouse in the north western bastion which contained a number of defensive features including eight murder holes. The lower levels of the outer wall have gun-loops or ports which provided flanking cover of the bottom of the moat. Walmer was linked to its sister castles of Deal and Sandown by a series of bulwarks, or earthen defences, built along the coast between them.
Since the early 18th century, Walmer Castle has been the official residence of the Lord Warden of the Cinque Ports. The alterations carried out during the 18th and 19th centuries were to create a residence in keeping with this role. One famous resident Lord Warden was the Duke of Wellington, who actually died at the castle.