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Grim's Ditch from Hampshire to Middlesex

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In southern England you can find a group of prehistoric earthworks running north from Hampshire and appearing in parts of Berkshire, Oxfordshire, the Chilterns and Middlesex, all variously named Grim's Ditch, Grim's Dyke or Grim's Bank. The spelling of Grim in older documents is Grimm or Grimes; they all refer to the same deity.

These are all separate earthworks, although in the past it was thought that some sections were at one time a continuous feature, but research into the nature of the monuments and the differing construction dates make this almost impossible. Explanations put forward for the purpose of the earthworks range from the use as territory or boundary markers to charge tolls on trade routes.

Grim's Ditch Hampshire

The best preserved and easiest to find is the 14 miles (23km), section of Grim's Ditch in Hampshire1.

The name Grim's Ditch is not the original name, if indeed it was ever named by its builders. It is thought they were probably named by early Viking settlers after the Norse god Grim, better known as the god Woden. This area was the original home of a people named the Dorsaetas. The Roman occupation would not have forced the original pre-conquest population to move from their ancestral homelands. The area may have been disputed with the Meonwara people from Hampshire as it is close to their mutual border. The first post-Roman Anglo-Saxon King of the area was Cerdic, who reigned from 519-534 AD. He claimed descent from the god Woden (Grimm). It is possible the Anglo-Saxons named the monument but it is more probable that it was the Vikings who were active in southern England after the death of Cerdic. They had a habit of naming landscape features after their gods. The Vikings appear to have given the name to many similar features in south east England.

The precise age of the Hampshire Grim's Ditches is uncertain, but they were all constructed in the period from the Bronze to the Early Iron Age. On a large scale topographical map Grim's Ditch appears as a spur running east from Bokerley Dyke into Hampshire. Another earthwork also named Grim's Ditch can be found in west Hampshire, close to Netherton Hanging Copse between the villages of Upton and Netherton. There is no evidence they were connected or constructed at the same time.

Officially classed as a linear earthworks, Grim's Ditches differ from their closest neighbouring earthwork Bokerley Dyke, which was constructed as a ditch with a single defensive bank behind. Grim's Ditches were constructed by digging a deep ditch originally approximately 2m deep and 4.5m to 6m wide and constructing a bank on each side of the ditch with the spoil. The differing construction styles in the various sections of the Grim's Ditch monuments do cast some doubt on their original purpose; the alternatives include a territorial boundary, defensive ditch or stock enclosure.

This Hampshire section, compared with the other earthworks of the same name, takes an unusual form for a defensive work. Originally a ditch between two banks, it appears more like a sunken trackway or cursus (see the notes below) than a defensive barrier. And neither side of this section of Grim's Ditch has an obvious defendable side. This appears to be a totally different type of earthwork from the other Grim's Ditches. A problem is the construction period; the Bronze Age to Early Iron Age is 1,400 to 3,000 years, or 23 to 50 generations. So archaeologists can only speculate who the builders were, and exactly when or why the monuments were built. There is the possibility that the monument(s) may have been modified by later people, who might at some point have altered or combined sections of the monuments for their own purposes.

Walkers may like to know that the long distance national footpath the Jubilee Trail runs close to the Hampshire section of Grim's Ditch for some distance as it crosses Martin Down, and it is worth taking a little time to see the monument.

The Landscape Around Grim's Ditch Hampshire

It is important when considering the construction of Grim's Ditch the intended use by the builders. There were at least 11 hillforts within a day's walk of the dyke and at least one settlement. This indicates a large population with farms and cattle, all of which would very possibly require protection from restless neighbours or invaders. The landscape was also very different, and large areas of forest stretching for miles covered parts of the countryside. These provided hunting grounds, fuel and building materials for the local inhabitants. Farming and the rearing of animals for food only flourished as the forest was cleared around the settlements. In some areas it is possible to approximate the date of the clearance (or absence of forest as in the case of moorland areas) of the forest by the appearance of stone as the main building material.

The Andredsweald Forest

One possible theory that probably explains why the monuments are fragmented and not continuous could simply be that the earthworks were built in unrelated sections as the forest was cleared by human activity. The ancient forests of southern England would have proven an almost impenetrable obstacle to an attacking army because of vulnerability to ambush by the defenders. So as forest clearance allowed passage through the forest, access points may have been fortified. The varying styles of construction may be attributable to the cultural differences of the peoples who built them.

The effect of the Anderida or Andredsweald2 Forest on the building of Grim's Ditch is worthy of consideration as it provides one plausible explanation of its fragmentary nature. One of the last remnants of wildwood in England, the forest was dense, dark and difficult to penetrate, the opposite of the New Forest3, which is open and flooded with sunlight for hunting game on horseback. But to the people of the late Bronze Age, the Andredsweald was probably the home of spirits, demi-gods and unknown terror.

The last records of the Andredsweald state that the forest stretched in an unbroken mass from Sussex, north of the South Downs, to Ashford in Kent. During the late Bronze and early Iron Ages it is likely that the forest stretched much further to the west, with north-south access provided by the valleys of the rivers Cerne, Piddle, Avon and Bourne. It was a formidable obstacle for any traveller or an invading army4.

Defended Settlements

  • Penbury Knoll Hillfort Map Ref: SU039171
  • Damerham Knoll Camp Hillfort Map Ref: SU099185
  • Colebarrow Hillfort Map Ref: SU033057
  • Frankenbury Hillfort Map Ref: SU167152
  • Gussage Hill Hillfort Map Ref: ST990140
  • Clearbury Ring/Clearbury Hillfort Map Ref: SU152244
  • Caesar's Camp/Bussey Stool Park Hillfort Map Ref: ST930156
  • Whitsbury/Whitsbury Castle Ditches Hillfort Map Ref: SU127196
  • Winklebury Camp Hillfort Map Ref: ST952218
  • Chiselbury Hillfort Map Ref: SU018281
  • Mistlebury Hillfort Map Ref: ST99581948


  • Martin Down Enclosure Settlement Site Map Ref: SU043200

    These sites would have supported an estimated population of between 10,000 to 15,000 or even more. There was an established leadership culture as indicated by the high status burial sites in the area. There are very likely more settlements in the area as yet undiscovered.

Monuments Located Within Five Miles of the Hampshire Section

It is important to remember that the landscape during the Bronze Age and Early Iron Age was very active and the surviving monuments provide evidence of this.

  • Bokerley Dyke5 is a linear earthwork; this differs from Grim's Ditch as it was constructed by digging a ditch and constructing a single bank on one side of the ditch with the spoil
  • Martin Down6 - Bronze Age Enclosure Settlement with ditch
  • Vernditch Chase7 - Long Barrows
  • Wor Barrow8 - Long Barrow on Oakley Down, noted as the first properly recorded excavation of a barrow in Britain.
  • Marleycombe Hill9 - Part of the Bowerchalke Downs including Woodminton Down and Knowle Down. A hilltop bowl barrow burial.
  • Pentridge Long Barrows - Numbered 1 to 4
  • Longbarrow House - Long Barrow
  • Blagdon Hill - A group of Round Barrows
  • Bottlebush Down - Barrow Cemetery
  • Scrubbity - Barrow Cemetery
  • Wyke Down - Round Barrows and Henge
  • Oakley Down Barrows - Barrow Cemetery
  • The South Down Ox Drove - Ancient trackway and Round Barrows

Other Earthworks Also Named Grim's Ditch

As previously mentioned the monuments may all have the same name due to the Viking settlers. Archaeological examination has concluded they were never connected as a continuous line. Some are generally regarded as to be insubstantial for defence; however, time and erosion may have made them less impressive. It is very possible they were used as territory markers, following tribal boundaries along the contours of the chalk uplands of southern England. Starting in the south the first section is located in Berkshire for a five mile (8km) stretch. There are two more sections named Grim's Ditches; the first is in Southern Oxfordshire running for five miles (8km), then in The Chilterns there is another stretch of 17 miles (27km). The final portion appears in Middlesex, running for two miles (3km) toward Harrow, near London. That is a total of 43 miles or 69km.

Grim's Ditch Berkshire

This section of Grim's Ditch in Berkshire stretches north east for five miles (8km), passing close to the villages of Ardington, Chilton and Hundred. The earthwork can be seen crossing the chalk hills of the Berkshire Downs. This section takes a more standard bank-and-ditch form. This length of Grim's Ditch now forms a part of The Ridgeway National Trail.

Grim's Ditch in Oxfordshire

The next length of Grim's Ditch is in southern Oxfordshire running for five miles (8km) from Mongewell to Nettlebed. If this was ever intended as a defence it would have protected southern Oxfordshire. Archaeological evidence indicates this section dates from the late Iron Age, possibly Roman.

Grim's Ditch in The Chilterns

In The Chilterns this part of Grim's Ditch can be traced for another 17 miles (27km). The southern end of this earthwork is at the village of Bradenham and proceeds north in sections as if a line of Morse code. The size varies so much that it is hard at times to remember it is the same type of monument, or built for the same purpose. The route continues north via Ivinghoe and Berkhamsted10 and terminates at the village of Potten End.

Grim's Ditch Middlesex

Another section appears in Middlesex, running for two miles (3km) from the Harrow Weald to Bushey Heath, near London. This is thought to be the youngest of the Grim's Ditch sections, and attributed to the Catuvellauni. This was possibly constructed as a barrier to the advance of the Romans' main invasion. This indicates that it was not originally part of the southern sections constructed in the Bronze Age and was simply named after them.

Lost Sections

There may have been more sections, now lost. There is a reference in a work by a Dr Plot in 1677 of a section of Grim's Ditch in Henley. This has now been lost, possibly under the expansion of Henley-On-Thames.

Why Were the Grim's Ditches Built?

The five Grim's Ditches have a combined length of 43 miles (69km), the origins and purpose of which are still obscure. Over the years there has been considerable debate regarding the purpose of the monuments. Most of it is about whether the sections or the ditches were ever connected as one monument. The two main factors against this are the sheer size of the project and the time they were constructed. The remaining sections, if connected, would be much more than 43 miles, but we do not know how much is missing. It has been suggested the River Thames would have been a likely end point for a line of defence. However what does rule out the possibility is that the period of construction of the various sections is so long at 1,400 to 3,000 years. Based upon the archaeological evidence the approximate construction dates of the Grim's Ditch earthworks are:

  • Early Bronze Age 2,500 to 1,500 BC11: The Chilterns.
  • Late Bronze Age 1,500 to 700 BC: Hampshire and Berkshire.
  • Iron Age 700 BC and after: Oxfordshire and Middlesex.
  • The evidence we have shows there is no possibility the sections could have been linked, except by name. They all vary in structure and design, fundamental things like bank size and positioning of the ditch. However, some variation in the surviving sections could have been caused by weathering, or problems in the landscape. The time available for the construction would also need to be taken into account. Different generations of builders is an explanation of the fragmented nature of the monument and the variation of design.

    Unfortunately much of what may have existed of the northern line of Grim's Ditch may have been obliterated by agriculture and residential development. This means that due to the lack of evidence we will never know why they were built, and they remain a landscape riddle.

    Notes: an Explanation of a Cursus Monument

    As the Hampshire section of the earthworks resembles a cursus monument a brief explanation of the term is necessary:

    A cursus is a Latin word, originally meaning a race course. It is a term describing a pair of parallel banks constructed by digging two ditches and piling the earth on the inside edges to form the banks.

    There are have been several of these monuments discovered in the area. Cursus monuments date from the late Stone Age and are thought to have been used as ceremonial or processional trackways or roads. They vary in width from 15 to 90 yards, and the lengths vary from 45 yards to over five miles. This type of feature always appears to have been constructed in relationship to burials or henges as part of a planned landscape. The best known example is probably the Stonehenge or Greater Cursus.

    Other local examples are:

    • The Dorset Cursus - the longest surviving processional trackway
    • Pentridge Cursus - a processional cursus
    • Gussage St Michael Cursus - a processional cursus

    1Grim's Ditch Hampshire at map reference SU056 51802.2Thought to mean black or dark oak wood.3A Saxon and Norman creation.4This is possibly why as late as 1066, King Harold chose Senlac Hill as a battle site, as the forest prevented his army from being encircled by the Norman cavalry.5Bokerley Dyke Dorset, another linear earthwork extending 3.25 miles (5.2km), at map reference SU05651802.6Martin Down Bronze Age Enclosure is at map reference SU043200.7Vernditch Chase is at map reference SU035204.8Wor Barrow is at map reference SU012173.9Marleycombe Hill is at map reference SU020226.10The Berkhamsted section is lost beneath the town and no longer exists.11These dates are the estimated dates for Britain. The earliest date of the start of the Bronze Age is in Mesopotamia in 2,900 BC.

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