Because the White Cliffs are the closest point to our continental neighbours, it has always been a key point in the defence of Britain's coastline. The oldest surviving fortification is the Iron Age rampart near Dover Castle, which would have looked out for threats such as the fleet of Julius Caesar in 55BC.

Dover - or Dubris as it was then known - became an important military base for the Romans. It was later used by the Saxons and Earl Harold built a stronghold there. After the Norman Conquest of 1066, William the conqueror ordered more fortifications to be built to consolidate his hold over the local Saxons.

By 1337 England was at war with France - just 21 miles away - and so the defences were increased again, most notably with Dover Castle which was built between the 12th and 13th centuries and became the largest castle in the kingdom. The ease with which the chalk could be tunnelled, led to many complex excavations, from medieval times right through to the Second World War and the cliffs are riddled with networks of tunnels and underground bunkers.