Summary.

This project attempts to interpret a potential Neolithic building from the excavated footprint of “Durrington 68” from Durrington Walls.  The design utilises known, but limited, carpentry evidence from the European Neolithic, in conjunction with modern and historical understanding of traditional building material properties.  

The proposed building design is constrained by several factors including;

1. The need for a functional educational space to be used by school groups and accompanying adults.
2. The need to marry the proposed building with the existing Stonehenge Visitor Centre site.
3. The limitations of incomplete archaeological remains.
4. The need to meet planning stipulations.

Where possible, direct archaeological evidence has been used to inform design choices, and where direct evidence does not survive, I have employed appropriate ethnographic and historical evidence in the choice and use of construction methods.

All materials are based on species lists obtained from Neolithic pollen samples taken from cores close to Durrington Walls.

Design Decisions 

• Roof Height:  The overall roof height of 6500mm for the proposed building is dependent on key factors including; The supposed wall height of the building, the overall dimensions of the archaeological footprint, and crucially, the choice of roof covering.  In this case, an appropriate roof covering for a building from this period, based on archaeo-pollen evidence from the area, would be domesticated cereal straw, grass, river sedge or rush.  All of these traditional roofing materials are applied to roofs with specific ranges of pitches to ensure their success.  Modern (medieval) thatching pitches tend to be at a minimum of 45 degrees, although some historic buildings can be slightly lower (at 40 degrees) or generally higher (between 50 – 55 degrees).  The proposed building exhibits a roof height that holds the roof pitch at between 40 and 45 degrees to ensure a good functional and long lasting roof.  Experimentally, the roof pitch (and therefore overall height) could be reduced, but the roof would become susceptible to leaks and rot, especially in the exposed weather of the Stonehenge Visitor Centre location.
• Wall Height and Construction: The overall wall height is constrained by factors such as the archaeological evidence of the excavated post holes at Durrington 68, and in this case, by the need to reduce the impact of the overall roof height.  In my opinion, the surviving posthole depth of Durrington 68 does not indicate the original placement of posts that were structurally free standing.  My interpretation of the relatively shallow (surviving depth) post holes, indicates posts that were short, or structurally connected to neighbouring posts in some way, or both.  Shallow set posts, individually weak, can be linked in a number of ways, including a timber wall plate that runs along their tops to form a very strong support for the eaves of a roof.  I have interpreted the Durrington 68 posthole evidence as the remains of such a wall.  The wall height is set at 1000mm to reduce the overall roof height to a minimum, while maintaining access to the outer wall surface for repair and maintenance.  It also prevents the temptation for visitors to climb on the roof.
• Building Form:  The proposed building attempts to marry the elements of the excavated footprint to produce a weather tight roof and usable internal space for educational groups.  The four internal post holes are best interpreted as a supporting frame for the roof weight above.  These substantial vertical posts are linked with a square purlin arrangement onto which a pitched roof rafter configuration rests.  The corners of this purlin square makes the construction of a conical roof problematic, and so I have blended a pitched roof  on the building sides, with conical roof construction at either end.  The internal space of the building is kept largely free to allow for the maximum usable space for education groups. 

Further Detail

Structural Interpretation and Discussion  

The evidence for a “Four Post” or “Square in Circle” structure is inherently interesting in terms of building evolution.  Our existing notion of building timelines starts with the amorphous ovate outlines of Palaeolithic “houses” or shelters, becoming more formalised in the clearly circular buildings constructed from mammoth tusk and other skeletal elements around 25,000 years ago.   

The rectangular and square forms of construction clearly evidenced in the earlier Neolithic (In both timber and adobe) seem to be a startling contrast to the known forms of building leading up to the development and widespread adoption of agricultural lifestyles.  

It would seem that the new demands of an entirely new subsistence strategy required a complete rethink of building style and scale.  This is unsurprising, given the vast requirements for storage, the rapidly expanding population of the agricultural world, and the need for habitual sedentary living.  

What is more surprising, is the gradual morphing of this earlier Neolithic rectangular model into more organic shapes exhibiting the use of generally small timber.  The monumentalism of Longhouses is replaced by a variety of generally smaller buildings that use generally smaller grades of timber.  It may be that this change reflects the widespread destruction of primeval forest, and the need to sustainably manage the remaining areas of woodland (producing pollarded and coppice timber rather than prime trees). 

We know that building forms become generally circular throughout the Bronze and Iron Ages, and reverts again to more rectangular forms during the Roman and post-Roman periods.  The temptation then, is to wonder if the evidence for Durrington 68 represents a middle ground between the “old” (the parallel paired posts of the Longhouse form), as seen in the square 4 post structure in the centre, and the “new” (the ovate, rounded form of the post built walls) rounded plan of the walls.  This may be overly simplistic, but the fact remains that a roof structure that sits on rounded walls and rests on a square frame, initially makes for an awkward, but not impossible roof interpretation.  The square frame that may have sat at the top of the 4 posts creates corners that are not easily overcome if we adhere to the idea of a conical formed roof.

Across the world, building forms reflect practical considerations such as material availability, but also the unseen cultural influences that also contributed to building style and function.  The combination of these factors results in unique building traditions, but also similarities across the world.  The availability, for example, of straight timber such as pine, inevitably encourages the use of that material in its most efficient form, although the scale and style of the finished building may differ dramatically across cultures.  

In the case of Durrington 68 I have to make certain assumptions before the design process begins.  

The first is that Durrington 68 does indeed represent the evidence of a building, and that as such, it has a roof and walls, along with at least one entrance.  It is not within the scope of this project to explore the many potential versions of the available evidence that might not represent a building for example.  My interest in this project is whether or not the evidence from Durrington 68 could be representative of a building, and if it can, what likely forms that building might have taken.  Of course, the project has its own set of constraints that will influence the outcome.

The ability to explore these questions is based on my understanding of archaeological evidence, natural material properties and evidence for ancient building and carpentry techniques based on research and my own experiments and traditional/authentic construction experience over the last 20 years.   

In terms of interpretation, it is important to say here that my ability to design a working building from the available evidence is not evidence that there was a “building” standing on the spot of Durrington 68 long ago.  It is a possibility, but there are other possibilities that might explain the same evidence in different ways.  The lack of basic evidence such as floors, hearths, timber remains and living debris, make a confident interpretation of this evidence impossible.  But as an exercise in experimental design, it is fascinating to see how the evidence would be best used to create a building if one had stood there originally.

What can we say?

Alignment

The axis of the building is aligned to the midwinter Solstice.  This evidence is in keeping with the majority of roundhouse structures and can be explained functionally or ritually.  Functionally, this alignment allows light to enter the building on winter mornings to illuminate the working interior, tracking slowly to maintain light levels around the eastern side of the structure.  The need for this light is confirmed in later structures (such as Must Farm) where the majority of possessions and utility equipment are situated on the eastern side of the building.

Outer Post Holes

The site has been heavily ploughed over the centuries and many features are truncated.  That said, obvious features remain in the form of outer and internal post holes.  

The outer post holes define the potential perimeter or wall of the building.  They range in diameter from 200mm to 320mm and survive to a depth of 180mm.  Although shallow, the effect of ploughing over centuries has surely reduced their effectiveness and depth as postholes.  It could also be argued that the measurements of the hole bases do not entirely reflect their original diameters accurately.  I think we could safely assume an original depth of hole at around 400mm if not a little deeper.  What is clear though, is that these holes were never very deep, and would not have offered solid cantilevering in the ground for them as tall individual posts.  

For me this evidence suggests, along with their close proximity to each other (somewhere between 500 and 800mm), that their placement relied on their neighbouring posts to offer structural support, and thus, the posts must have been structurally joined or linked in some way.

This could be achieved by linking the posts along their tops using an interlocking wall plate, or by joining them by woven pliable rods (using the posts as the uprights for a continuous woven hurdle wall), or by a combination of the two.  From experience, the curve of the post hole line, and its gapping of around 500mm lends itself to the weaving, in situ of pliable wands harvested from willow or hazel trees.  This evidence reflects similar curves and stake-hole gapping in building 851 from Durrington, which was successfully reconstructed using a basketry technique to form its walls by our team during the “Neolithic Houses Project”.  

The post hole diameter suggests original post diameters of between 100 – 200mm.  This would still allow sufficient gap around the positioned post to effectively tamp the back-filled soil to create a sound footing.  

In my mind, the surviving depth of these post holes precludes them as having been free standing palisade posts of any imposing height.

The gap in outer post holes on the eastern side of the plan may represent a real gap in the original structure, or represent more aggressive truncation by ploughing in this area.  In my opinion, and given the nature of holes 209 and 211 that seem to mark an entrance way at the south eastern end of the structure, the gap in the outer post holes does not represent an intentional opening.  I would expect an intentional  gap of 3400mm in a structure of this scale to be marked by larger postholes, indicating the placement of larger posts to support the weight of a lintel and the significant roof weight above that span.

For this project I propose to fill this gap with further post holes of appropriate depth and width to enable the continuation of a supported wall plate at this point.

Internal Post Holes

Six features are clearly defined within the outer post hole line.  Four of these (29, 30, 31, 32) form a square setting of around 6500mm width.  They survive to a depth of around 1400mm and suggest an original depth of significantly more (possibly 1800mm).  

These steep sided, flat based holes are ideal to house substantial vertical posts (perhaps 400mm in diameter) that provide excellent structural support for a substantial roof structure and weight above.  Their depth would suggest the need to house (and provide cantilevering for), tall posts, perhaps up to 5500mm to 6500mm.  This in turn would create an incredibly tall roof height (potentially between 8500mm and 10500mm) that would have a serious impact on the Durrington landscape.  

Although these post holes would allow individual posts to stand securely, the square plan suggests strongly to me that they were related structurally, and joined in some way to produce a substantial supporting frame for the roof weight above.  This would be best achieved by placing an interlocking purlin square at their tops that would offer options to further support a rafter structure and thatched roof.

Features 33 and 34 have been identified as pits or possible post holes.  For me, their symmetry and placement at the end of outer post hole lines, strongly indicates their use to house uprights associated with an entrance in the south east end of the structure.  Their diameters of around 1300mm would allow a substantial pair of posts to sit here (perhaps over 600mm diameter) and support a lintel that would in turn support the rafter ends over the doorway.  There is potential here to produce a monumental doorway that reflects the scale of the internal structural frame.

My interpretation of this evidence, with the proviso that it was a building, creates the potential for an architecturally imposing structure of significant height that would have presented a very different aspect to our traditional views of Neolithic buildings.  It presents an exciting prospect for the construction of such a building as a Learning Space.

Design Constraints and Considerations

The design of a building that best fits the limited available evidence is further constrained by essential design parameters.  

1. A building with a thatched roof.  The desire for an authentic style building requires the use of thatch material as the roof covering.  Pollen evidence from Durrington Walls during the late Neolithic period offers materials such as rush, water reed and cereal straw as likely options.  The use of thatch brings with it demands to maintain a roof pitch of certain minimum angles to ensure a watertight covering.  In modern thatching practice, 45 degrees is considered the absolute minimum for a thatch angle, although experimentally, thatching of reconstructed structures varies from 38 degrees upwards. The need to maintain a steeper roof pitch has an effect on the overall height of a building in relation to its wall height and building diameter and directly affects the building aesthetic.
2. Overall height.  This project will sit close to the existing Visitor Centre at Stonehenge and is expected to have to sit below the height of the south pod roof line at 7000mm.  This constraint directly affects the ability to replicate a full scale Durrington 68 structure and maintain tolerable thatching angles.
3. Educational provision.  The building must meet the brief of accommodating an education group of 30+ children, plus accompanying adults, plus English Heritage volunteers in a flexible learning environment.  It must also provide storage for session equipment, be accessible, and have adequate head height for occupants.  The nature of this educational experience demands more space than usual in a formal learning environment, where students are largely static during their tasks.  These requirements promote the idea of a Durrington 68 type structure at full scale.
4. Workforce.  The nature and high profile of this project lends itself to engaging volunteers as the main workforce.  The techniques and materials required during construction are outside the experience of most contractors, and in my experience, a volunteer workforce can learn and develop these skills to a high standard during progressive project phases.  A volunteer workforce is a difficult thing to quantify however, and so construction timetables must allow for a certain degree of flexibility.  All of my previous projects using volunteer workforces have run according to schedule, but a risk remains that a volunteer workforce may experience unforeseen issues. 

Appropriate Evidence for Durrington 68

This project is rooted in the limitations of available Neolithic evidence for building construction.  Ironically, some of the best evidence for Neolithic carpentry in Europe comes from chronologically older sites (5000bc) than Durrington Walls (2500bc), in Germany and Switzerland. 

As experimental archaeologists, we are forced to use what little physical evidence there is to draw sweeping conclusions about the standard of Neolithic construction.  The lack of physical construction evidence is bolstered by our current evidential view of the Neolithic world, supplemented with assumptions based on circumstantial evidence.

The image below shows a surviving Neolithic well lining from Germany, and offers us an insight to the sophistication of Neolithic carpentry.  This well lining is built from split planks, that have been adzed to shape using polished stone tools.  The planks are joined at their corners using “Tusk Tenon” joints and held in place with tapered locking pegs.

The importance of this evidence cannot be overstated in terms of carpentry understanding by its makers in the early Neolithic.

This method of jointing timber is still used today in some carpentry applications, but in a Neolithic context, reflects some of the limitations of tool type on required tasks.  A tusk tenon joint allows for an initially loose fit (a tight fit is very difficult – but not impossible to achieve, using stone and bone chisels), that can then be locked in position by the insertion of a long tapering peg that acts to stabilise the entire joint.  

This evidence clearly illustrates the ability and skill of Neolithic builders to join large timbers together using recognisable carpentry methods.  It also shows their ability to fell and process large trees into smaller workable timber using radial splitting strategies to produce elements such as planks, and therefore, beams, joists, lintels, rafters etc.

The use of cross lap joints to locate boards above the tusk tenoned base frame also shows a complete understanding of structural need.  The foundation is carefully crafted, providing the ability to take less time on subsequent layers of boards.

The work is expedient but, although superficially rough, this evidence opens our eyes to the potential levels of finishing in Neolithic carpentry and construction tasks.  This well lining acts as a revetment  to the surrounding earth and gravel, and was produced with the knowledge that, once installed, it would never be seen by its users.  Despite this fact, many of the planks exhibit good levels of finishing with both stone and bone tools.  We can only guess at the levels of finish exhibited on the structural elements of houses which would have been viewed daily. 

At this point we must carefully consider the specific nature of this evidence.  It would be wrong to assume that this level of carpentry and precision was the limit of Neolithic construction knowledge, given its specific application.

A further example of surviving Neolithic carpentry comes from Zurich, in the form of a plank built door recovered from fine lake sediments.

This door represents high levels of carpentry skill in an object that was clearly intended to be seen and used daily.  Made from Black Poplar, three planks have been split from a log, shaped to create thin and light boards, carved to create timber bosses that have then been mortised to allow the positioning of hazel runners that join and lock the three boards together.  It is a fine example of complex carpentry and deep material knowledge.  Each wood type is chosen for its unique properties.  The joints are cut with precision and the resulting door is a triumph of design and construction process.

Further evidence for carpentry and construction sophistication comes from the Stonehenge itself.  This stone monument clearly exhibits mathematical understanding in its layout and plan (let alone the requirements to predict the seasonal movement of the sun).

But it also demonstrates jointing techniques that are directly relevant to this project.   

The precision and engineering demonstrated in these stone joints is obvious and must reflect some of the ideas and methods employed in large timber constructions produced in the same period.

This evidence is appropriate to a reconstruction of Durrington 68, as it is unlike the Neolithic Houses (house 851) reconstructed at the Stonehenge Visitor Centre in several crucial ways.  The first difference is scale.  The floor plan of Durrington 68 is around six times larger than building 851.  This immediately requires larger timbers to span increased distances.  

The second difference is the evidence for a square large timber post configuration at its centre.  The testing of this evidence as a building requires these large timbers to be structurally related to each other.  This requires jointing and carpentry techniques to be employed.  Unlike the small houses, which we interpreted as relatively simple structures with driven stake foundations, using the pliable nature of available coppice material to make them strong, Durrington 68 requires a different level of construction complexity.  

The third difference relates to roof weight and outer wall construction.  The Neolithic Houses were possible with simple woven walls with thin pliable rafters that slotted into the wall tops.   The relatively low roof weights enabled light woven roof members to be used.  The spans and roof weights in any reconstruction of Durrington 68 will require a more serious outer wall structure to bear its weight with rafters securely located at the outer wall top.  

Using this Neolithic evidence, combined with knowledge of material properties that was well known into the historical period, and which must have been passed from generation to generation through time, we have a basic inventory of techniques and design options with which to develop our building design for Durrington 68.