[6] The castle lighthouse survived after being converted into a belfry in the Saxon era (c. 1000), having a new upper layer added (c. 1430), and was partially renovated in 1913–1915.

The scant remains of the other Roman lighthouse, known as the Bredenstone or the Devil's Drop of Mortar, are located on the opposing Western Heights, across the town of Dover.

[8] The Roman lighthouse at Boulogne-sur-Mer across the Channel, known as the Tour d'Ordre, survived for many centuries, and its light should have been visible from Dover.

Suetonius refers to Caligula's "erection of a tall lighthouse, not unlike the one at Pharos, in which fires were to be kept going all night as a guide to ships".

From the Cinque Ports foundation in 1050, Dover has always been a chief member—it may also have been this that first attracted William's attention, and got Kent the motto of Invicta.

William Twiss, the Commanding Engineer of the Southern District, as part of his brief to improve the town's defences, completed the remodelling of the outer defences of Dover Castle by adding the huge Horseshoe, Hudson's, East Arrow and East Demi-Bastions to provide extra gun positions on the eastern side, and constructing the Constable's Bastion for additional protection on the west.

Twiss further strengthened the Spur at the northern end of the castle, adding a redan, or raised the gun platform.

The solution adopted by Twiss and the Royal Engineers was to create a complex of barracks tunnels about 15 metres below the cliff-top, and the first troops were accommodated in 1803.

[24] The outbreak of the Second World War in 1939 saw the tunnels converted first into an air-raid shelter and then later into a military command centre and underground hospital.

In May 1940, Admiral Sir Bertram Ramsay directed the evacuation of French and British soldiers from Dunkirk, code-named Operation Dynamo, from his headquarters in the cliff tunnels.

[23] A statue of Admiral Ramsay stands outside the tunnels in honour of his work on the Dunkirk evacuation and protecting Dover during the Second World War.

[23] This plan was abandoned for various reasons, including the realisation that the chalk of the cliffs would not provide significant protection from radiation, and because of the inconvenient form of the tunnels and their generally poor condition.

[29] Dover Castle remains a Scheduled Monument,[30] which means it is a "nationally important" historic building and archaeological site that has been given protection against unauthorised change.

[34] In October 2021, the castle was one of 142 sites across England to receive part of a £35 million grant from the government's Culture Recovery Fund.

[41] The medieval setting has also been used in films such as Lady Jane (1986), Hamlet (1990), To Kill a King (2003), The Other Boleyn Girl (2007), Into the Woods (2014), and Avengers: Age of Ultron (2015).