would originally have had an earth mound built up against the base of it to protect against attack, and the stone work remains rougher in the first few courses of masonry. Around the keep is an essentially square structure guarded by three large towers, all built during the 1280s from somewhat darker sandstone. On the more vulnerable southern and eastern sides of the castle, ditches 27 metres (90 ft) long and 9 metres (28 ft) deep have been cut into the rock, exploiting a natural fissure. These towers have large "spurs", resulting from the interface of a solid, square-based pyramid with the circular towers rising up against the walls. This feature is characteristic of castles in the Welsh Marches, including St Briavel's and Tonbridge Castle, and was intended to prevent the undermining of the towers by attackers. The castle's fourth corner forms its gatehouse. Here the classic Edwardian gatehouse design has been transformed into an asymmetrical structure, with one tower much larger than the other. The gatehouse included portcullises, murder-holes and a drawbridge. Beyond the gatehouse lies a large barbican, inspired by a similar design of the period at the Tower of London and possibly built by the same workmen, designed to protect the causeway leading to the gatehouse. The barbican today is only half of its original height, and includes its own gate, designed to trap intruders within the inner defences. The gatehouse and barbican are linked by a stone causeway. The gatehouse's eastwards-facing tower contains the chapel, an unusual arrangement driven by a lack of space, with a recently restored east window of reset 15th-century glass designed by Nicola Hopwood, which illuminates the priest's seat, or sedile. The 15th-century window frame itself replaced an even taller, earlier 13th-century window. The chapel's west window is modern, and commemorates the British scientists, engineers and servicemen involved in radar development who died between 1936 and 1976. The altar itself is particularly old, possibly pre-dating the castle. The bailey was designed to include a number of spacious domestic buildings. These include a great hall, a solarium, kitchen, buttery and pantry, with a luxuriously large number of garderobes and fireplaces. The large towers provided additional accommodation. The design of the domestic buildings was skilfully interlocked to support the defensive arrangements of the bailey. The great hall for example, , was placed in the strongest position overlooking the river Wye, allowing it to benefit