Dover Castle was originally an Anglo-Saxon fortification, built around a Roman Pharos and the Saxon church of St Mary in Castro. In 1066, after the battle of Senlac, William of Normandy founded an earth and timber post-Conquest fortress, before moving on to London. In the late 12th century, King Henry II founded the stone concentric castle, when adding a monumental keep, which is still defended by its inner bailey curtain wall and parts of the outer bailey curtain wall. In the 13th century, the castle's defences were strengthened and the accommodation modernized. Sadly by the 17th century, the castle was dilapidated but still used as a prison, until the mid 18th century, when the defences were again modernized. During the Napoleonic Wars, additional gun batteries and outworks were installed and an extensive network of underground communication and accommodation tunnels were excavated. The castle was used during World War I and in World War II, anti aircraft and search light batteries were constructed. No castle in England is larger or has a longer history. 7 miles north-east is Walmer Castle.