Ancient Monuments

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

A Scheduled Monument in Eartham, West Sussex

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Latitude: 50.8794 / 50°52'45"N

Longitude: -0.6929 / 0°41'34"W

OS Eastings: 492051.521011

OS Northings: 109692.424919

OS Grid: SU920096

Mapcode National: GBR DG9.ZJV

Mapcode Global: FRA 96FS.3W9

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

Scheduled Date: 13 December 1978

Last Amended: 7 March 2002

Source: Historic England

Source ID: 1020514

English Heritage Legacy ID: 29283

County: West Sussex

Civil Parish: Eartham

Traditional County: Sussex

Lieutenancy Area (Ceremonial County): West Sussex

Church of England Parish: Boxgrove

Church of England Diocese: Chichester


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
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.

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.

Source: Historic England

Reasons for Scheduling

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.

Source: Historic England


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

Source: Historic England

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