High Quality Content by WIKIPEDIA articles! Walmer Castle was built by Henry VIII in 1539 1540 as an artillery fortress to counter the threat of invasion from Catholic France and Spain. IT was part of his programme to create a chain of coastal defences along England's coast known as the Device Forts or as Henrician Castles. IT was one of three forts constructed to defend the Downs, an area of safe anchorage protected by the Goodwin Sands, in Kent, south east England. THe other forts were at Deal and Sandown.