Causewayed enclosure, World War II searchlight emplacements and associated remains on Halnaker Hill


Heritage Category: Scheduled Monument

List Entry Number: 1020514

Date first listed: 13-Dec-1978

Date of most recent amendment: 07-Mar-2002


Ordnance survey map of Causewayed enclosure, World War II searchlight emplacements and associated remains on Halnaker Hill
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The building or site itself may lie within the boundary of more than one authority.

County: West Sussex

District: Chichester (District Authority)

Parish: Boxgrove

National Park: SOUTH DOWNS

National Grid Reference: SU 91964 09601, SU 92046 09693, SU 92057 09807


Legacy Record - This information may be included in the List Entry Details.

Reasons for Designation

Between 50 and 70 causewayed enclosures are recorded nationally, mainly in southern and eastern England. They were constructed over a period of some 500 years during the middle part of the Neolithic period (c.3000-2400 BC) but also continued in use into later periods. They vary considerably in size (from 0.8ha to 28ha) and were apparently used for a variety of functions, including settlement, defence, and ceremonial and funerary purposes. However, all comprise a roughly circular to ovoid area bounded by one or more concentric rings of banks and ditches. The ditches, from which the monument class derives its name, were formed of a series of elongated pits punctuated by unexcavated causeways. Causewayed enclosures are amongst the earliest field monuments to survive as recognisable features in the modern landscape and are one of the few known Neolithic monument types. Due to their rarity, their wide diversity of plan, and their considerable age, all causewayed enclosures are considered to be nationally important.

Despite some disturbance by modern ploughing, the causewayed enclosure on Halnaker Hill survives well, and partial excavation has shown that it retains archaeological remains and environmental evidence relating to the construction and original function of the monument. Use of the exposed hilltop for flour milling during the post-medieval period illustrates a then common, everyday activity of which only a limited number of visible remains survive. The continuing strategic importance of the hill into the 20th century is represented by the World War II searchlight emplacements. Identified as a troop headquarters, the partly ruined emplacement is a powerful reminder of a crucial episode in the defence of the Channel coast.


Legacy Record - This information may be included in the List Entry Details.


The monument, which falls into three separate areas of protection, includes a Neolithic causewayed enclosure, a later post mill and World War II searchlight emplacements situated on a chalk spur which projects to the south from a ridge of the Sussex Downs. This location enjoys panoramic views of the surrounding countryside and the Channel coast to the south. The causewayed enclosure is a NNE-SSW aligned, oval area of about 2ha surrounded by a low bank up to 5m wide and 0.5m high. The bank is flanked by an encircling ditch up to 4m wide and 0.1m deep. Ploughing in the 20th century has partly levelled the boundary earthworks, particularly on the northern side of the enclosure, where the bank survives as a scarp up to 0.4m high. The main access to the interior of the enclosure was by way of a simple, inturned entrance through the southern defences, and at least five other original gaps through the boundary earthwork have been identified. A further, north east-south west aligned linear bank, now largely levelled by modern ploughing, runs alongside and to the south west of the north western side of the enclosure, and this has been interpreted as an original, associated feature. Investigations between 1981-1983 led to the discovery of fragments of pottery within the ditch. Some of these have been dated to the Neolithic period (3500-2000 BC), and Late Bronze Age and Roman sherds indicate that the enclosure may have undergone subsequent episodes of reuse. The later post mill lies close to the southern entrance of the earlier enclosure and survives as a roughly circular mound about 19m in diameter and up to 0.8m high, with a large central depression. Historical records suggest that the windmill was sited here in 1540 by the Duke of Richmond in order to operate as the feudal mill for the Goodwood Estates. In about 1850 the post mill was replaced by a tower mill constructed about 25m to the north west. This circular tower mill, which is Listed Grade II, is built of bricks faced with clay tiles and has a restored timber beehive cap and four sweeps. The tower stands on a terraced, circular earthen platform about 25m in diameter. The windmill fell into disuse after being struck by lightning in 1905 and suffering severe storm damage in 1913. It was comprehensively renovated in 1934 and restored again in 1950. The tower mill was used as an aircraft observation tower during World War II. Associated with the tower mill and roughly contemporary with it is the site of the miller's house, which survives as a roughly rectangular building platform up to 13.5m long and about 9m wide terraced into, and thus partly disturbing, the south eastern ramparts of the earlier causewayed enclosure. An embanked, circular depression about 12m in diameter and 0.6m deep situated about 25m north east of the tower mill represents a now dry dew pond dating to the 18th or 19th centuries. During World War II, four large searchlights used to seek out raiding enemy aircraft were sited on the hilltop. The searchlight emplacements, the middle two of which are situated within the earlier enclosure, were constructed about 100m apart in a south west facing, semicircular arc. They are octagonal structures about 6m in diameter with concrete foundations and mortar-brick or red brick walls. Apart from the southernmost, which has been largely dismantled and takes the form of a concrete foundation, the emplacements survive to their full height of 2.6m. The northernmost emplacement has been capped with modern concrete and is used as a reservoir. Within the interior are the circular concrete foundation blocks on which the now removed searchlights were mounted. A rectangular concrete platform within the eastern sector of the earlier enclosure would have supported an associated military structure. The tower mill, Ordnance Survey triangulation pillar and all modern fences, gates and stiles are excluded from the scheduling, although the ground beneath these features is included.

MAP EXTRACT The site of the monument is shown on the attached map extract. It includes a 2 metre boundary around the archaeological features, considered to be essential for the monument's support and preservation.


The contents of this record have been generated from a legacy data system.

Legacy System number: 29283

Legacy System: RSM


Books and journals
Oswald, A, Dyer, C, Halnaker Hill, West Sussex, (1995)

End of official listing