Reasons for Designation
Linear boundaries are substantial earthwork features comprising single or
multiple ditches and banks which may extend over distances varying between
less than 1km to over 10km. They survive as earthworks or as linear features
visible as cropmarks on aerial photographs or as a combination of both. The
evidence of excavation and study of associated monuments demonstrate that
their construction spans the millennium from the Middle Bronze Age, although
they may have been reused later.
The scale of many linear boundaries has been taken to indicate that they were
constructed by large social groups and were used to mark important boundaries
in the landscape; their impressive scale displaying the corporate prestige of
their builders. They would have been powerful symbols, often with religious
associations, used to define and order the territorial holdings of those
groups who constructed them. Linear earthworks are of considerable importance
for the analysis of settlement and land use in the Bronze Age; all well-
preserved examples will normally merit statutory protection.
The boundary known as the Buckinghamshire and Hertfordshire Grim's Ditch
includes numerous surviving sections from within three main linear earthworks
aligned along the Chiltern Hills between Bradenham and Berkhamsted and
spanning a total distance of 18km. It does not appear that these principal
sections were ever joined to form a continuous boundary. Current evidence
suggests that the sometimes quite sizeable gaps represent areas which were
formerly forested or in which natural features served to perpetuate a
division of the land. The same pattern has been discerned along the North
Oxfordshire Grim's Ditch, to the west of the Thames. A further comparable
linear boundary, the Moel Ditch, extends to the east across parts of
neighbouring Bedfordshire.
For the most part the visible sections of Grim's Ditch in the Chilterns
include a wide single ditch, flanked by a bank of upcast earth, which is
always upslope of the ditch. Other features, discovered by limited
excavations include a turf core within the bank, a berm separating the
bank and ditch (concealed over time by the spread of the bank material)
and a trench for a fence or palisade along the outer rim of the ditch.
The Buckinghamshire and Hertfordshire Grim's Ditch is thought to have
served as a territorial boundary, separating, and perhaps enclosing,
organised groups of land and settlement. It may also have been an
agricultural boundary, denoting grazing areas and impeding the movement
(or theft) of stock. Excavations to date have provide only limited dating
evidence. Pottery recovered from the fill of the ditch indicates that it
was in existence in the Iron Age. As such, the boundary provides important
evidence for the management of the landscape in the centuries preceding
the Roman Conquest in AD 43, although it may have a considerably earlier
origin. It remained a notable feature in later centuries, acquiring its
present name (a variation on the name of the god, Odin) at some point in
the early medieval period, perhaps during the period of Pagan Saxon
settlement in the 5th and 6th centuries. The earliest recorded use of the
term `Grim's Ditch' occurs in a charter granted by Edward, Earl of
Cornwall in 1291.
All sections of the Buckinghamshire and Hertfordshire Grim's Ditch which
survive in visible form, or as well-preserved buried remains (identified
by aerial photography or ground survey), are considered integral to a
general understanding of the monument and will normally merit statutory
protection. The section of Grim's Ditch in Oaken Grove survives well as a
visible earthwork along most of its length and provides a fascinating
insight into the nature of early territorial land division in the Chiltern
Hills. It will contain archaeological evidence for the manner of its
construction as well as environmental evidence for the appearance of the
landscape in which it was built. The archaeological evidence may also
include artefacts or scientific dating material from which to determine
the period of its construction and the duration of its maintenance as an
active boundary.
The two mounds built over this section of Grim's Ditch are thought to mark
the location of post mills, a common form of windmill in the medieval
period consisting of a wooden superstructure which rotated around a
central vertical post. The central post was mounted on cross timbers
stabilised by being set into a mound. This mound might be newly built, but
earlier mounds were also reused. The whole superstructure of such a mill
was rotated to face into the wind by pushing a horizontal pole projecting
from the mill on the opposite side from the sails. The end of the pole was
supported by a wheel and rotation eventually resulted in a shallow ditch
surrounding the mill mound. Post mills were in use from the 12th century
onwards. No medieval examples of the wooden superstructures exist today,
but the mounds, typically between 15m and 25m in diameter, survive as
field monuments. In general, only those mounds which are components of
larger sites or which are likely to preserve organic remains will be
considered worthy of protection through scheduling. However some mills
used earlier earthworks, such as castle mottes and burial mounds, which
are worthy of protection in their own right.
The two mounds overlying Grim's Ditch in Oaken Grove are extremely well
preserved and will contain a range of archaeological evidence for their
construction and uses. The most likely remains are those of the mill
structures which the mounds are thought to have supported in the medieval
period, although the possibility of evidence of earlier ritual or funerary
origins is an important consideration. The proximity of the two mounds to
a similar earthwork 800m to the south west is of particular interest. This
earthwork, `Danes Camp', is thought to have originated as a small motte
castle in the 11th or 12th century but is also thought to have been
converted to support a post mill. All three sites utilise the exposed
location above the dry valley to the north and appear to represent a
sizeable agricultural regime without recourse to water power.
Details
The monument includes a 245m length of the prehistoric boundary known as
the Buckinghamshire Grim's Ditch running broadly north west to south east
along the southern edge of Oaken Grove, a small woodland area on high
ground to the south west of Hampden Bottom. The monument also includes two
mounds, built over the line of the prehistoric earthwork, which are
thought to mark the location of medieval windmills.
The section of Grim's Ditch in Oaken Grove survives as a clearly visible
bank and ditch along most of its length. The earthen bank measures up to
7m wide and stands up to 0.8m high in some places. To the south of the
bank lies a parallel ditch, approximately 9m wide and despite centuries of
silting up to 0.8m in depth. Excavations carried out in 1973 and 1991
along other sections of Grim's Ditch in Hertfordshire produced evidence of
a level area, or berm, separating the bank and ditch. Evidence for a
palisade trench, which would have supported a wooden fence was also found
along the outer edge of the ditch. Similar components may also survive as
buried features along this section of the Grim's Ditch.
Towards the south eastern end of this section of Grim's Ditch there are
two mounds approximately 40m apart on the line of the boundary, truncating
the bank. The section of Grim's Ditch between the two mounds has been
disturbed and survives as a shallow earthwork. These mounds clearly
post-date the construction of the prehistoric boundary and have revealed
pottery fragments which suggest a medieval origin. The most likely
explanation is that they represent two contemporary or successive medieval
post mills. It is possible, however, that the mounds have an earlier
origin, perhaps as paired Roman or pagan Saxon burial monuments, and were
adapted to support windmills in this favourable exposed location. The
mounds are similar in appearance. Both overlie the line of the bank and
are steep sided and circular. The eastern mound measures approximately 28m
and 3m high; that to the west 22m by 2.5m. Both mounds are encircled by 8m
wide ditches cut through the earlier earthworks (presumably to provide
building material for the mounds) leaving narrow causeways to the north
west and south east. The western ditch is seasonally waterlogged. The
summits of the two mounds are marked by depressions. The scar on the
western mound is small and may indicate the collapse or removal of a
central post. The hollow on the eastern mound is much larger, 10m in
diameter, and may mark the site of a undocumented antiquarian excavation.
A further section of Grim's Ditch exists to the north west, near Hampden
House Lodges. This section and others along the entire known route of the
boundary are the subject of separate schedulings.
All fences and fence posts 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.
