Known as the key to England, Dover Castle has been in our nation’s first line of defence, guarding our shores for 20 centuries. In the 13th century, King John built underground tunnels connected to sally ports to surprise attacking troops

February 29, 2024

Known as the Key to England, Dover Castle has been in our nation’s first line of defence, guarding our shores for 20 centuries.

Exploring GB

Dover Castle commands the Strait of Dover, the shortest sea crossing between England and continental Europe, a position of strategic importance throughout history.

Castle Hill was shaped into massive defences capped by medieval walls and towers and later, from the mid 18th century, by the earthworks of a garrisoned infantry and artillery fortress.

Beneath the surface, cut into the chalk of the North Downs, are networks of tunnels to enable the garrison to move, plan and live in safety.

Exploring GB

The network of tunnels served as a barracks for soldiers during the Napoleonic Wars and became a headquarters and hospital during the Second World War.

The origin of settlement on Castle Hill, where Dover Castle stands, may be in the pre-Roman Iron Age.

The irregular shape and massive enclosed area of the castle earthworks are not typically medieval, more closely resembling a hillfort.

In southern England, hillforts were built from about 500 BC until the Roman invasion, variously as places of permanent habitation or of refuge.

The castle visible today, however, was established by Henry II (r.1154–89), in the decade 1179–89. He spent lavishly, creating at Dover the most advanced castle design in Europe.

Exploring GB

His engineer, Maurice, built the inner bailey and towers, part of the outer bailey and a huge centrepiece – the immense great tower, a sophisticated building that combined defence with a palatial residence.

With no substantial properties in Kent, Henry needed a magnificent and impressive setting in which to receive and accommodate important visitors making the journey.


In 1204, King John (r.1199–1216) lost the Duchy of Normandy to the French king, Philip II (r.1180–1223), resulting in enemy territory just across the Channel.

This prompted more expenditure at Dover, furthering the design of Henry II in the outer wall and towers, and royal accommodation in the inner bailey.

This was the castle that resisted determined sieges in 1216 and 1217 during the First Barons’ War (1215–17), when King John fought against a coalition of English barons and Prince Louis, heir to the French throne.

Exploring GB

The castle garrison, led by Hubert de Burgh, repulsed all attempts to take the castle, though the barbican and main gate at the northern end were severely damaged.

When war ended in 1217, building resumed for Henry III (r.1216–72).

The vulnerable north gate was blocked solid and replaced by two more: the main one at Constable’s Gate on the west side, also a residence for the castle constable, and a secondary one, Fitzwilliam Gate, on the east.

The builders remade the barbican and cut a tunnel under the outer wall to reach it, via the new St John’s Tower that dominated the outer ditch, and a covered passage across it.

The passage continued as a tunnel under the Spur, where it divided into three, allowing defenders to defend the barbican.

Exploring GB

Building continued sporadically under Henry III into the middle of the 13th century.

By this time the castle had reached a peak of development, as one of the largest and most sophisticated castles in Europe. It included a royal residential complex lining the walls of the inner bailey.

In 1265, the castle was besieged again, with Eleanor de Montfort in residence.

After the death of her husband at the Battle of Evesham during the Second Barons’ War, there was a short siege at Dover, ended by negotiation with Eleanor and her nephew, the Lord Edward (son of Henry III).

Dover remained important under the Tudors, especially after Henry VIII (r.1509–47) built artillery forts in Dover and along the south-east coast in 1539–40.

The Holy Roman Emperor, Charles V, came to the castle in 1522 and met Henry there, at the start of a six-week diplomatic visit.

Exploring GB

The great tower’s royal apartments were refurbished to receive Anne of Cleves on her way to marry Henry in 1539.

Elizabeth I (r.1557–1603) visited in 1573 and ensured the castle was kept in good repair during the war with Spain in the final two decades of the century.

Royalty last used the castle in 1625, when the great tower received a makeover for the French princess Henrietta Maria, on her way to marry Charles I.

Thereafter the king’s favourite, the Duke of Buckingham, made alterations in the great tower and to some buildings in the inner bailey.

Afterwards the castle was neglected, playing no significant role during the Civil Wars of 1642–5.

Exploring GB

The great tower was used as a prison for French and Spanish prisoners during the Nine Years War (1688–97) and the War of Spanish Succession (1701–14), and their graffiti can be seen on its walls.

World WarsWhen Britain declared war on Germany on 4 August 1914, Dover Harbour became the home of the Royal Navy’s Dover Patrol to defend the Dover Strait, particularly against German submarines, and to protect communications for the Army in France and Flanders.

Dover had a garrison of around 16,000 troops, with the castle as headquarters, to defend a perimeter occupying the high ground around the town for up to 1.5 miles distant.

Within the perimeter were many training camps for soldiers destined for the Western Front.

The harbour approaches were defended by coast defence guns, while the new threat from airships and airplanes was addressed by anti-aircraft guns, including two near St Mary in Castro.

Exploring GB

Entry to the harbour was regulated and the control building, the Fire Command Post (established in 1905) and Port War Signal Station (1914), survives in Dover Castle, with a commanding view over the Channel.

The Cold War

The Army vacated the castle in 1958, except for Constable’s Gate which remained as a senior officer’s residence until 2015.

In the early 1960s, the government selected Dover Castle as one of 12 Regional Seats of Government, to be occupied in the event of nuclear war.

It was to be in the charge of a senior minister, with a military and civilian staff, tasked with creating some form of administration after a nuclear attack.

The heart of this was in Dumpy level, with Annexe refitted as a dormitory and the western tunnels of Casemate repurposed as dormitories, dining and catering areas and rest rooms.

Exploring GB

The complex was sealed against contamination and given air filtration and communications equipment including a small radio broadcasting studio. It was decommissioned in the early 1980s.

Today, the castle is a popular tourist attraction, currently maintained by England Heritage.

You don’t need to book your ticket in advance, but you will always get the best price and guaranteed entry by booking online ahead of your visit.

Someone who recently visited the castle said: “For anyone with an interest in history, this is a whole day occupation – and even then you may not see it all!

”If your interest is purely Second World War, there is a good half day with plenty of authentic artefacts and reconstructions, plus the Napoleonic era tunnels reused for WWII.

Exploring GB

”Though there is a good map, the site as a whole is not as self explanatory as I had expected, so I wish I’d bought the guide book.”

If you enjoyed this blog post, please follow Exploring GB on Facebook for daily travel content and inspiration.

Don’t forget to check out our latest blog posts below!

Thank you for visiting Exploring GB.