Dover Castle was built in the 11th century and is the largest castle in England. It’s also referred to as the “Key to England” due to its defensive significance throughout history.
During the Iron Age, the site may have been fortified with earthworks (there is evidence of unusual patterns in its foundation). The site of Dover Castle also contains one of only three surviving Roman-era lighthouses in the world, a 5-level 8-sided tower built in the early 2nd century.
William the Conqueror defeated King Harold and turned to Dover. He took the town, burned it, and built fortifications there before heading to London for his coronation.
The Castle was first built, entirely out of clay. It collapsed to the ground and the clay was then used as the flooring for many of the ground-floor rooms. (Words of William of Poitiers)
It was, however, during the reign of Henry II that the castle began to take shape as we recognise it today. From 1179 to 1188, the King spent the enormous sum of over £6,500 on the castle. The fortifications kept growing under King John, who establishes the first royal fleet and completes the castle’s outer defences, and Henry III.