Fort for the defence of London.
The London Defence Positions were a late 19th century scheme of earthwork fortifications in the south-east of England, designed to protect London from foreign invasion landing on the south coast. The positions were a carefully surveyed contingency plan for a line of entrenchments, which could be quickly excavated in a time of emergency. The line to be followed by these entrenchments was supported by thirteen permanent small polygonal forts or redoubts called London Mobilisation Centres, which were equipped with all the stores and ammunition that would be needed by the troops tasked with digging and manning the positions.
This particular monument includes the main compound of Fosterdown Fort, also known as Pilgrims Fort, situated on a southern spur of the North Downs, around 1km south of Caterham. The main, south facing compound, is roughly circular in plan and is defined by a large, earthen rampart. The shallow, surrounding ditch, which is in turn encircled by a low bank, contained spiked metal railings which completely enclosed the compound. Access to the interior is from the gorge to the north or rear of the compound through a gap in the rampart, which is flanked by low concrete walls which meet its rear-curving ends.
The entrance is approached by a track from the north, and opens onto an almost square, north west-south east aligned central parade. Its concrete walls, on the north eastern and western sides, extend to join the low gorge walls. The parade is defined on its south western side by a three roomed magazine, set into the rear of the forward rampart, just below the internal ground level. To minimise the risk of explosion, the magazine chambers were lit by lamps, set in recesses behind panes of glass, and accessed from the lamp passage which surrounds the magazine. The corridor in front of the chambers was divided into two sections by the addition of a partition wall. The short passage in front of the cartridge store contained a shifting lobby, just inside the entrance, where magazine personnel changed into protective and non-spark producing clothes. A separate entrance for the two shell stores, in the south eastern portion of the magazine corridor, also provided access to the lamp passage and two small chambers designed to store lamps and fuses. On either side of the partition wall, the outer wall of the corridor is pierced by two issuing hatches, through which ammunition was passed outside for collection.
The magazine retains many of its original features, including two windows facing into the parade, and wooden shutters in the ceiling of the shell stores, designed to control the circulation of air through the ventilation ports. A four roomed casemate block, set into the rampart just below ground level, defines the south eastern side of the parade. At each end of the casemates, steps lead up from the parade onto the top of the rampart, which could function as a firing parapet, allowing the mobilisation centre some degree of self-defence in the event of enemy bombardment.
After the London Defence Positions were abandoned, in around 1905, the centre was finally sold in 1920. It was subsequently used, for much of the 20th century, as a field study centre for school groups. To meet their needs, the casemates were converted into washrooms and drying rooms, and two brick chimney stacks were constructed on the flat roof, above the ventilation shafts. Associated with the main compound are the original, semi-detached pair of caretakers' cottages and the mobilisation tool store, situated on the eastern side of the approach road from the north.
The mobilisation tool store, which is Grade II Listed, located just outside the entrance is now the main residence This building is therefore not included in the scheduling. A number of features within the area of the monument are excluded from the scheduling. These are: all modern fences; all modern fixtures and fittings, including all components of the modern electrical and plumbing systems, as well as modern materials and equipment stored within the mobilisation centre; and the wooden sheds, constructed on the north eastern edge of the rampart and ditch. The ground beneath these items is included in the scheduling, together with structures and surfaces related to the military use of the site, to which some of these features are attached.