Historian Sam Willis charts the stories of Britain's castles and their roles in the country's history, art and literature. He begins by looking at the structure's first appearance during Norman rule in 1066, and then at the siege of Kenilworth Castle 200 years later, revealing how it was initially used as an instrument of invasion, but soon became a weapon with which unruly barons challenged the crown. He also visits Tintagel Castle in Cornwall, the place where King Arthur is said to have been conceived