Dover Castle probably originated as a motte and bailey castle, built after the Norman Conquest of 1066. Its unusual outline may be due to the reuse of the ditch and bank of an Iron Age hillfort (see record 468006) as well as parts of the earlier Saxon burgh (see record 467951). Dover Castle was transformed by King Henry II and Maurice 'the ingeniator' supervised much of this work between 1179 and 1188: building the keep, the walls of the inner bailey and parts of the outer curtain wall. When the castle was completed, it was the first in Western Europe to have concentric layers of defence around a central keep.
The outer curtain wall was completed and a number of D-shaped towers were built in 1204. The unsuccessful siege of 1216 by Prince Louis, prompted a programme of modernisation, supervised by Hubert de Burgh, from 1217 to 1257. This included the construction of St John's Tower and the main entrance, Constable's Gate. During the 15th century the castle was an administrative centre for the Cinque Ports. However by the 17th century Dover Castle had fallen into ruin. Its small royal garrison was captured at the start of the Civil War and it was used in the 1680s to 1749 to hold French prisoners of war.
However, from 1740 its decline was reversed and JP Desmaretz supervised a programme of modernisation. Defences were strengthened and barracks built. The most important changes took place during the Napoleonic Wars, between 1793 and 1815. Lieutenant Colonel William Twiss, oversaw the bomb proofing of the keep, and added gun batteries and outworks. Underground tunnels for communication and accommodation were also dug.
From the 1850s the castle was adapted to modern warfare. The castle was rearmed in the 1870s and was used during World War I and World War II. A tunnel system (see record 468096) housed various naval and coastal headquarters and played an important part in coordinating the Dunkirk rescue.