The Story of London Season 1 Episode 5 Castles

The building of a defensive line of castles like the one at Lewis along the coast of Dover was William the Conquerer's way of making sure his retreat was secure. Lewis Castle, built about 1000 years ago, is a prime example of shutting the door behind yourself and making sure its bolted closed. William went on to secure land all over Europe and established 36 castles thus fortifying his kingdom.