03 March, 2011

Debunking the myth of timber circles

The Myth
In archaeology there is the evidence, and there are the opinions put forward to explain and connect it.

In the highly subjective world of archaeological opinion, it has become widely accepted that the concentric rings of prehistoric postholes, once thought possibly to be buildings, were the freestanding timber equivalents of Neolithic stone circles.
These ‘timber circles’ have become central to modern understanding of ancient landscapes, as realised by Time Team. [1] Recently, Professor Vince Gaffney has even detected a ‘Timber Stonehenge’ [2].
They account for some important archaeological sites including Woodhenge, Durrington Walls, and The Sanctuary, and are even found in the Iron Age.
In 1996, Tim Darvill called these structures Type Ei buildings, [3][above left]. However, once others, particularly Alex Gibson, ventured the opinion they were too large to be roofed, they became ‘Timber Circles’ [4]. Many academics have long since moved off to explore this strange freestanding ‘ritual’ landscape, although, officially, it appears that the jury is still out:
“A timber circle is the foundation of a large wooden structure comprising a series of two or more roughly concentric rings of postholes which once supported substantial timber uprights variously interpreted as stanchions of a roofed building or freestanding posts. Timber circles are generally over 20m in diameter and the individual postholes are typically over 0.5m across.”
English Heritage web site. [5]
Actually, they are not too big, but entirely consistent with the scale other large oak timber roofs, and this can be demonstrated because they were made from trees.

Please click to enlarge the drawings, and consider them; they form an important part of an argument, which centers on how to understand archaeological site plans.

The Reality

In comparison to medieval roofs, they are not too wide, and have considerably more supporting posts; most are 50' /15.24m wide or less. Westminster Hall, a timber roof on stone supporting walls, with no posts, is 68’(20.72m) wide. [Above].

In essence, most type Ei buildings took the form of a very wide Neolithic longhouse with a central supported ridge and a symmetrical arcade and roof plates. They usually comprise five concentric rings of posts, forming an annular shape. These posts are arranged to support a polygonal ridged roof that narrows on the inside and widens on the outside.
How the center worked is more difficult. Some, like Woodhenge, with a centre narrow enough to be roofed, have an extra sixth set of posts inside the middle ring.

The middle ring, making the ridge of the roof, has the largest, deepest postholes, as these posts would be the tallest vertical components of the building. The postholes become progressively shallower away from the ridge, marking the shorter posts supporting the arcade and roof plates.

Traditional timber buildings were made from the trunks of oak trees, the growth pattern of which is broadly predicable [right]. In general terms, the longest usable tapering timber that these trees will produce, neither too fat at one end, nor too thin at the other, straight and without branches, is about 50’/15.24m. The availability and natural limits of these trees can be optimised through managed woodland, but ultimately they dictate the scale of individual timber components, such as rafters and ties.
A tie is a piece of timber running across the base of a roof constraining the outward forces in a large roof. It is subject to the same limitations as other timbers, and this in turn, limits the width of the roof. This explains why these structures, like other large timber roofs, including Iron Age Roundhouses, are limited to about 50’ wide.
This is not the only factor affecting scale in timber buildings, and like all architectural limits, it must expected that it will be pushed. At the same time, since a 50’ timber is probably comparatively rare, that available for ‘ordinary buildings’ will be significantly smaller, in the 30–40’ range.
The posts supporting a 50’ tapering tie should be large at one end and small at the other; this explains why the postholes of the outer rings are larger than the inner ones [above]. If all the horizontal timbers are placed with their thin end pointing inwards, this will simplify the assembly of the frame, avoiding having to join components of radically different thickness. This is also reflected in the generally smaller postholes on the inside of the middle ring.

A 50’ tie would require support at least at one point, and so, if you draw in the line of a tie between corresponding posts [holes] in the outer and inner ring of a class Ei building, you will find it will usually pass next to one, or more, internal posts. Looked at in more detail, because there are a greater number of outer posts than inner ones, a pattern of radial ties, laid out much like a bicycle wheel, is evident. [Left]
Interlace theory takes these ideas much further, beyond the effect of the tapering timber on the plan, into the detailed structure and geometry of the roof.
These are some of the largest timber post structures in prehistory, so it is entirely appropriate these buildings are constructed at the limits of design, and not beyond it. Each example is individual, and clearly the product of architectural and building techniques used to furnish large roofed structures where society and individuals required it.
Understanding in conflict with belief
‘Timber circles’ actually are buildings, as Professor Darvill suggested fifteen years ago, the posthole foundations of top-of-the-range oak timber architecture. With building, as with most crafts, some clients demand the best available, which in architecture is often the biggest, tallest, or widest. Admittedly, they are complicated and not straight-forward, but that is precisely because they are big buildings made from hundreds of tapering tree trunks.
This explanation requires no belief, only understanding. It accounts directly for all the basic characteristics of the evidence, explaining the size, depth, and distribution of the postholes. It does so in terms of the typical form of the trees evident in the construction, and their position in the geometry of the structure.
Trying to connect these complex timber structures with circles of stones, largely on the basis that they are both circular, does not really wash as grown up argument. It has led to much barking up the wrong trees, and the myth of timber circles, a tale that has grown much in the telling, so much so that those who say “archaeologists make up stories about the past” may have cause to feel vindicated.[6]

Sources and further reading

[1] http://www.channel4.com/history/microsites/T/timeteam/2005_durr.html [accessed 6/03/2011]
[2] http://www.telegraph.co.uk/science/science-news/7903824/Ancient-wooden-version-of-Stonehenge-found-on-Salisbury-Plain.html [accessed 6/03/2011]
[3] ’Neolithic houses in northwest Europe and beyond’’ (1996) Neolithic Houses in North-West Europe and beyond (Oxbow monograph 57) [Paperback]. T.C. Darvill (Editor), Julian Thomas (Editor) [Fig 6.9]
[4] Gibson, A. 2005. Stonehenge and timber circles (revised 3rd edition). Stroud: Tempus Alex M. Gibson
[5] http://www.eng-h.gov.uk/mpp/mcd/sub/timc1.htm [accessed 6/03/2011]
[6] http://www.timeshighereducation.co.uk/story.asp?storycode=404899 [accessed 6/03/2011]


Odin's Raven said...

Why were they circular, rather than more usual rectangular buildings?
What were they used for - clan dwellings, public buildings such as sports stadia or markets or theatres? Was something being maximised or minimised - heating costs or storage volume or something?

Geoff Carter said...

Hi OR, thanks for the comment.I have discussed some of the advantages of round buildings in post 23, but my guess is they were trying to maximize the accommodation space in the roof, by increasing its hight and width.

How and for what they were used for is more difficult to establish, and it must be considered on a case by case basis in the light of the site's archaeology, as well as the nature of the building[s].
The key issue is, who had access to the considerable resources required to build a large timber buildings?

I can objectively prove that Woodhenge is a building, this is not an opinion; I also think it is probably a EBA Wessex culture palace - but this is just my opinion.

Odin's Raven said...

Thanks Geoff. I can understand round buildings with concentric rings as imitations of sacred space, where the centre is the most exalted;but the big egos who build palaces, they certainly like to be at the 'centre', but also like to have everything 'lead up to' them. Hence, I wonder whether these buildings dominate the landscape from one direction, with an avenue of approach and lines of trees, amidst hunting parks and flower gardens. On a circular model, perhaps there would have been increasingly rarefied zones between the outside world and the sacred ruler.

A palace would have lots of servants, guards and courtiers living in it, but how would the zones of prestige and access have been managed? Perhaps there was a visual class system, with upper, middle and lower classes on the various floors!

Perhaps the king liked to keep close to the taxes, so a reason for emphasising volume might have been that it was also a barn, and he lived on top of the taxes, which he could distribute to his followers.

Maybe the ground floor was for animals, and the people lived over them. I wonder if it was a sort of combination of the Scottish vitrified brochs, and the 'Stables of Solomon' underneath the temple in Jerusalem.

Geoff Carter said...

Hi OR,
I have said this many times;just because things are the same shape does not make them equivalent. Archaeology is far too dependent on looking for, finding, and thinking about shapes.
'Sacred space', is quite a difficult. However, it is seems clear than in the first millennium bc, living in circular buildings, [or perhaps buildings that were not square], had become a cultural trait in Britain and Ireland.
Animal downstairs and people above is the normal arrangementin much of Northern European vernacular architecture.
Scale probably reflect both the size of the 'household', and status.
Quite why large buildings are built depends really on who's doing the building; elites and aristocracy have entirely different concepts of architecture and its utility.

I have a bias towards hierarchical societies in this period, but as you point out, there is a wide range of communal uses for roofed space in a more complex society.

Odin's Raven said...

If these big buildings were scarce and expensive, I wonder if there was a specialised group of carpenters who went from site to site, like the medieval masons.

Probably people could only afford one big building per community, so it would have had multiple uses, like medieval churches. As a palace it might not have been heavily inhabited all the time, but the king might have 'held court' there seasonally, to feast and to transact any public business. Presumably this would have attracted entertainers and peddlers as well as litigants and the socially ambitious, and have provided 'all the fun of the fair' for the locals.

I wonder if the plan was based around a central hearth, like a gigantic hut. That could explain why it was circular - and also why it had to be high, so that the fire would not set the roof ablaze. Thus most of the storage space might only have contained hot air; perhaps with galleries at higher levels, rather than floors right across the centre. Maybe it was a bit like Elizabethan theatres, where the 'quality' in the upper tiers could watch the groundlings and players in the centre.

I suppose there must be some scientific ratios between size of building and size of fire it could safely contain, and it would not be surprizing if these people had a good practical optimization of building size and cost with the comfort of the most users. I wonder whether any sign was found of stone hearths or fire ditches at the centre, or whether any ashes and charcoal, bones etc would have survived in the vicinity.

I remember long ago pausing for a few minutes at Woodhenge, to read about it and wonder what the field of concrete stumps could possibly have been. Thank you for providing a good explanation.

Geoff Carter said...

Hi OR,
The Historical/cultural tradition in Britain, is political control by a small elite or aristocracy; communal activity is facilitated by the elite, and they usually controlled and initiated the major components of built environment.
It is easy to get side tracked in archaeology by looking to explain our buildings in terms of peoples with a different cultures, environments, and raw materials to explain our archaeology.
To the best of my knowledge none of the structures in Britain was built by, or influenced by, North American natives, East Africans, or Madagascans.

Thinking in terms of what buildings were built in the historical record is probably instructive.
For example, as you note, seasonal use is a feature of royal palaces; The Queen's summer palace Balmoral, started life as a hunting lodge.

Incidentally, any building that dumps all it's waste in its immediate environment will become uninhabitable. On high status sites having the waste moved to middens some distance away, might be expected.
As you say, fires are very important, but the word hut is inappropriate;remember, the fireplaces are probably not on the ground floor, making their detection difficult.

The idea that all [later Iron Age] roundhouses had a central fire on the ground floor is not supported by the evidence. It's a nice image, but it's not true, a gross over simplification ate best, it is just another peer reviewed myth - like 'Timber Circles'.

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Gordon Clarke said...

I know that this is now old and I am necroposting but hey this is archaeology and what is a couple of years in the scale of things?? So a few points from an architects point of view.

1. Is there any evidence for the use of oak? It is a mighty difficult timber to work without sharp metal tools?

2. There is no reason why any timber needs to be longer than the span between three posts. Medieval roofs may have a single long principle, but traditional roofs are frequently constructed with short rafters spanning between purlins. So you cannot determine anything by the size of trees.

3. You cannot assume that there was a ridge above the sturdiest posts - this is a critical assumption you appear to have made. There are plenty of buildings which use this ring for a heavy ring of purlins off which the roof is cantilevered.

4. The pitch of the roof may or may not have been as steep as you show it. Is there any evidence for this? It may even have been flat - I have seen some large communal structures with grids of posts joined together almost flat and with layers of earth and turf on top.

5. Are you really suggesting that in this period people had timber floors with fires on them?

6. You should not rule out the value of looking around the world - it is a useful place to find simple practical solutions that people have developed, and there may be more in common between rural Africa and Bronze Age Britain than between the Bronze age and the Medieval periods here.

just my 2p of peer review. I am not saying you are wrong in any of it, but I am starting to realise that a completely cross disciplinary approach is needed to solve these questions.

best wishes


Geoff Carter said...

Hi Gordon, thank you for thought provoking comments, which I will address point by point.
1] When oak is green is much easier to work, and only becomes very hard as it dries out and ages. Experimental archaeologists have tried out ancient tools on wood, and on those rare occasions when structural wood has been found it is usually oak.
2] Medieval roof are a different type of technology, reflecting several millennia of technical development; clearly a roof is more than its principle rafters, and the spans are determined by the position of the posts – this is deductive analysis. This has to be seen in terms of Neolithic approach to roofing.
3] It is not the sturdiness of the posts [diameter] but the depth that is indicative of height in this context.
4] Timber Buildings in this country [& N Europe] No there isn’t where traditionally thatched a steep angle to keep them watertight and shed snow, etc.
5] Yes – they had clay hearths on timber floors or how could you build piled buildings on lakes – a practice from the earliest Neolithic times.
6] No, Africa has termites, and imo has no similar timber frame building tradition. The whole approach is about reverse engineering from the archaeological evidence, and understanding building as a culturally specific technology.
Interdisciplinary approach fantastic - but a dream
At Newcastle University I never met anyone who even knew what a "Tie" was - let alone what it did - otherwise my life could have been entirely different!

Geoff Carter said...

Thanks for the comments.
The geometry of the cone and cylinder are very important in understanding circular structures; I covered much of this in an earlier post;
My late-lamented PhD had a chapter of graphs exploring these properties, however the the key issue in this context is what happens when you scale up simple designs. There is a natural limit to scale of these structures, which become very complex to assemble with the materials available in prehistory.

Please note that "Iron Age" buildings have been constructed since 1940's!] 1970's as reproductions of African Houses in local materials, and are NOT representative of the archaeological evidence. They are a form of entertainment

As for cosmic alignments, it is probably only solar festivals like the the Solstice that would be significant, these can be observed through a window or door.

The bluestones at Stonehenge would appear to be a stone circle relocated into a building held up in its second phase by sarsen pillars as well as the usual timber posts.

Where does it say that religion in Britain involved waving at the sky?
... By and large it is an indoor activity; one of the most difficult aspects of archaeology is separating the "pictures of the past" in your own head - which are all entirely imaginary, from the actual archaeological data.