Buckinghamshire Grim's Ditch: 245m long section in Oaken Grove with two associated post mill mounds, 235m south east of Briary Cottages


Heritage Category: Scheduled Monument

List Entry Number: 1021197

Date first listed: 19-Aug-1936

Date of most recent amendment: 24-Feb-2004


Ordnance survey map of Buckinghamshire Grim's Ditch: 245m long section in Oaken Grove with two associated post mill mounds, 235m south east of Briary Cottages
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The building or site itself may lie within the boundary of more than one authority.

County: Buckinghamshire

District: Wycombe (District Authority)

Parish: Great and Little Hampden

National Grid Reference: SP 85535 02015


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

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.


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


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

Legacy System number: 35338

Legacy System: RSM


Books and journals
Network Archaeology, , Grim's Ditch: Archaeological and Management Survey Phase III, (1999)
Burgess, B, 'Records of Buckinghamshire' in Earthworks at Hampden and Little Kimble, (1855), 138-139
Burgess, B, 'Records of Buckinghamshire' in Earthworks at Hampden and Little Kimble, (1855), 138-9
Renn, D F, 'Antiquity' in Mottes - A Classification, , Vol. 33, (1959), 16
Bronze Age round barrow,
Bucks County Museum (32.57)(box 98), Med. pot from mounds,
SM:27132, Went, D , Motte Castle known as Dane's Camp 400m south of Hampden House, (1996)

End of official listing