Built by William II in 1092, the castle served to prevent Scots raiders getting through. The Norman keep was altered in Tudor times to accommodate cannons to replace archers. The visit also takes in the Warden's quarters, where Richard III stayed, the prison, with its walls covered in astonishing graffiti (15C) and the Cumbria's Military Museum. A feature of the outer ward is the half-moon battery, which was built c 1540 to facilitate the deployment of cannons.