Castle Town

Caerphilly Castle comprises a set of eastern defences, protected by the Outer East Moat and the North Lake, and fortifications on the Central Island and the Western Island, both protected by the South Lake. The site is around 30 acres (120,000 m2) in size, making it the second largest in Britain. It is constructed on a natural gravel bank in the local river basin, and the castle walls are built from Pennant sandstone. The castle's architecture is famous and historically significant. The castle introduced concentric castle defences to Britain, changing the future course of the country's military architecture, and also incorporated a huge gatehouse. The castle also featured a sophisticated network of moats and dams, considered by historian Allen Brown to be "the most elaborate water defences in all Britain".

The eastern defences were reached via the Outer Main Gatehouse, which featured circular towers resting on spurred, pyramidic bases, a design particular to South Wales castles. Originally the gatehouse would have been reached over a sequence of two drawbridges, linked by an intervening tower, since destroyed. To the north side of the gatehouse was the North Dam, protected by three substantial towers, and which may have supported the castle's stables. Despite subsidence damage, the dam still holds back the North Lake. The South Dam was a massive structure, 152 metres (499 ft) long, ending in a huge buttressed wall. The remains of the castle mill – originally powered by water from the dam – survive. Four replica siege engines have been placed on display. The dam ended in Felton's Tower, a square fortification designed to protect the sluicegates regulating the water levels of the dam, and the South Gatehouse – also called Giffard's Tower – originally accessed via a drawbridge, which led into the town.