Since the English Channel was first formed 10,000 years ago, the White Cliffs of Dover have loomed in front of invaders and travelers from the continent at the crossing’s narrowest point. It was an obvious place for a medieval castle, and a particularly large and magnificent one, 375 feet (114 m) above sea level; but the oldest survival is a lighthouse built by the Romans soon after their conquest of Britain in the first century c.e. It is possibly Britain’s oldest building still standing.
The Saxons fortified the site with earthwork ramparts, ditches, and wooden palisades. They also used Roman bricks in the seventh century to build the church of St. Mary in Castro, heavily restored in the 1850s. The defenses were improved by William the Conqueror, but the main stone fortifications date from Henry ll’s time, with a huge keep with walls up to 22 feet (7 m) thick and a double line of encircling walls. In 1216 the castle was held for King John against the rebel lords and an army of French invaders. Later modifications include some made by Henry VIII, and a 23-foot- (7-m-) long bronze cannon that he installed, known as “Queen Elizabeth’s Pocket Pistol.” Some of the rooms have inscriptions scratched on the walls by foreign prisoners of war held in the castle in the eighteenth century.
Concealed inside the White Cliffs is an intriguing labyrinth of tunnels, first built during the Napoleonic Wars and intended for cannons to repel Napoleon’s threatened invasion. This never materialized, but the tunnels came into their own in World War II when they were extended and used as the headquarters of Operation Dynamo, the Dunkirk evacuation.