Tags: construction, dolmen, Neolithic
I went to a lecture recently (Wednesday 10th December 2014) given to members of the Royal Archaeological Institute (RAI) at Burlington house in Piccadilly. The lecture was entitled: ‘Building the great dolmens: monumental construction in the early Neolithic of Britain and Ireland’ and was presented by Dr Vicki Cummings from the University of Central Lancashire.
Dolmens (old term: ‘cromlechs’) are neolithic structures typically consisting of a single large capstone held aloft by three smaller upright stones.
The following is my recollection with additional observations, thoughts and ideas. I apologise in advance to Dr Cummings for any errors in my recollection, understanding, or interpretation.
She began by stressing the shift of emphasis away from the traditional names of ‘portal tombs’ or ‘dolmen tombs’, to simply dolmens (for reasons explained later). She also made reference to chamber tombs, and the distribution of dolmens across Britain and Ireland and over time.
Geographically, the dolmens that survive to the present (and have been identified) seem to cluster in Kent, Cornwall, Pembrokeshire, Anglesey and then more prolifically around Ireland. Dr Cummings made the point that the dolmen tradition was imported from the continent. The distribution on her map, revealed that almost all are ‘coastal’, which suggests the neolithic builders were coastal dwellers and spread by sea.
My own very cursory research reveals that the greatest concentration of neolithic dolmens is in Korea, with more in southern India, the Horn of Africa, throughout the mediterranean, up into Russia and across Europe. Again, the distribution suggests seafaring.
Temporally, the oldest dolmens appear to be in western Europe and are about 7,000 years old. The ones in Britain appear to have been in use from c.4,000-1,000BC. To my modern sensibility, used to the disposable and a fast pace of change, it is amazing to imagine that anything made by us would be utilised for 3,000 years. Of course, it’s possible that the structures changed use over time but it’s tempting to imagine a belief system, or tradition, that had a degree of continuity over such a long period (Christianity has lasted 2,000 years, so there’s precedent).
Based on a wider survey of dolmens, Dr Cummings proposed that the traditional emphasis on the ‘portal’ or ‘chamber’ aspect of these structures is misplaced and should rather be on the capstones. The reasons for this being the observed pattern of such capstones almost always being disproportionately huge in relation to their supports and to any supposed use as a mere roof i.e. the size of stone is not a necessary mechanical function.
The huge mass of these stones (up to 150 tonnes), and the concomitant effort needed to raise them, suggests that this achievement over mass may have been the symbolic virtue/purpose of these structures.
She also made the point that there were almost always three supporting stones and they were, generally, as slender as possible.
To me, this combination of forms conveys many messages at once. It illustrates strength in small size, of the great being supported by the small, of the power possible through cooperation, and the need for or power of balance. In essence: ‘we are small but together we can achieve great things’. Of course, many other messages may have been conveyed, with obvious candidates being the boundary between elements with death as the vehicle between, the ancient sanctity of the number three, ‘earth’ element/spirit raised to ‘sky’ element/spirit (perhaps to mate? perhaps with fire or blood as a spark of life?), domination of the land, marking one’s territory (‘this land is ours’), and leaving a legacy (‘remember, I/we lived once’). All very speculative, of course.
The primary focus of Dr Cummings’ lecture was the work that she and Colin Richards had done on one particular dolmen: Garn Turne in Pembrokeshire, Wales. She described it and the archaeology they undertook. Amongst the questions that arose was, of course, that of construction techniques.
My immediate thought was ‘counterweight’.
Ever since I discovered that counterweights are what enable lifts to work (lifts are what made skyscrapers practical; early lifts were hydraulic e.g. St.Pancras) I’ve been delighted by the notion of them – pure magic to be able to shift a vast weight with the touch of your finger (assuming perfect balance of components). Since then, I’ve been alive to them. Hearing Dr Cummings’ description of the site and how pre-civilised landscapes were strewn with rocks, it seemed obvious to me that the neolithic builders must, surely, have used some of these boulders to build up counterweights to the capstone and so facilitate its movement.
A counterweight is used to partially, or totally, reduce the weight of the object that needs moving. It does this by attaching the object, via a pivot (e.g. A-frame), to another weight. The greater the counterweight, the easier it becomes to move the object (see end for evidence for neolithic counterweights).
The 80-ton capstone at Garn Turne would be a lot easier to raise if some, or all, of its weight were offset by a counter made from the abundance of smaller stones strewn locally. The limitation of this method is the breaking-strain of the ropes.
Neolithic people used a huge variety of raw materials to make ropes but the best available for this period is lime bark cordage. This was used across northern Europe from 9,000-3,000BC. It has a wet breaking strain of 2,830 Newtons (c.315Kg but not clear for what size rope). It performs best in water, is rot resistant, and floats, so our seafaring/coastal dwelling neolithic dolmen builders are likely to have known it.
Ways to overcome breaking-strain limitations include using several ropes (with safety benefits for sudden rope failures), and/or several separate counterweights used in unison, each optimised to the breaking-strain of the rope and pivot. The only limitations then become space to operate, manpower, and time.
Another method that may have been used concurrently is that only one end of the 80-ton capstone was lifted at a time meaning far less to raise. Once the end was raised, it could be shored up with timber, or stone, and then the process repeated to raise the other end.
Dr Cummings’ suggestion was that the capstone was excavated and as space was made under it, stones were forced in under it. In my cursory research I happened across a reference to a modern analogue that supports this incremental approach (see end).
A feature that leapt out at me, when she mentioned it, was the finding of two shafts dug under the stone that Dr Cummings described as too small for an adult but large enough for a child. My immediate thought was that this was a channel for passing ropes through to then allow the stone to be levered and pulled up. However, in answer to my question, Dr Cummings stated that the channels did not meet.
However, on reflection, it seems to me that these shafts could have accommodated tree trunks used to ‘see-saw’ buried stones out of the ground. A trunk inserted into such a shaft and resting on a pivot (stone or wood) could have counterweight stones added to the exposed end to aid lifting. Again, the limitation is the breaking-strain of the trunk, so more than one would be needed (two shafts at Garn Turne).
All these methods are complimentary and I see no reason why they couldn’t have been employed concurrently. They all seem viable and contemporary.
Anyway, just a potted account of a lecture, plus the ideas it spawned, mixed with no more than a dash of very superficial research. So, plenty of scope for error but hopefully of interest nevertheless.
Lime bark cordage
Oldest counterweights: ‘The oldest known balances are of lever type symmetrical balances. A symmetrical balance beam made of limestone older than 3000BC was found in Egypt.’
Shadoof: There is also evidence for the use of counterweights in ancient Egypt and India. These ‘shadoofs‘ were used to raise water for irrigation. However, it should be noted that simple mechanisms and advances can occur independently in any location. Shadoofs have been used in northern climes to draw water from frozen lakes (as in Estonia).
Counterweights at Cissbury Ring: ‘…four pear shaped lumps [of chalk] pierced at one end and with signs of wear from some cord being threaded through it. These may have been used as a counterweight for some sort of pulley system to take materials and waste to the surface, though three more have been found in shallow pits on the surface near a piece of carved bone reckoned to be part of a loom, leading to the interpretation that these are loom weights.’
4720±150BP (3900-3030 Cal BCE)
4650±150BP (3780-2920 Cal BCE)
4730±150BP (3910-3040 Cal BCE)
Digging out boulders: ‘Living in rocky New England, my mother-in-law and I had to use ingenuity to move a huge underground stone in order to plant a straight row of border hemlocks on our property. I would not say we were muscular types, but my elderly neighbor showed us how to dig a small hole next to the boulder, toss in stones, dig some more, toss in a few more stones, until we actually made the bolder pop out of the ground.’
Neolithic stone construction at Stonehenge:
Great animation (no audio) illustrating how the experts commissioned by English Heritage (custodians of Stonehenge) believe the stones were constructed and raised. Shows the use of levers, pivots and A-frames but, no suggestion of counterweights. I simply cannot understand why such a simple, useful and contemporary mechanism is not included in the proposal.
Other near-contemporary construction techniques: Levering methods are considered to be the most tenable solution to complement ramping methods, partially due to Herodotus’ description; and partially to the Shadoof; an irrigation device first depicted in Egypt during the New Kingdom, and found concomitantly with the Old Kingdom in Mesopotamia. In Lehner’s (1997: 222) point of view, levers should be employed to lift the top 3% of the material of the superstructure. It is important to note that the top 4% of this material comprises 1/3 of the total height of the monument. In other words, in Lehner’s view, levers should be employed to lift a small amount of material and a great deal of vertical height of the monument.
In the milieu of levering methods, there are those that lift the block incrementally, as in repeatedly prying up alternating sides of the block and inserting a wooden or stone shims to gradually move the stone up one course; and there are other methods that use a larger lever to move the block up one course in one lifting procedure. Since the discussion of construction techniques to lift the blocks attempts to resolve a gap in the archaeological and historical record with a plausible functional explanation, the following examples by Isler, Keable, and Hussey-Pailos list experimentally tested methods. Isler’s method (1985, 1987) is an incremental method and, in the Nova experiment (1992), used wooden shims or cribbing. Isler was able to lift a block up one tier in approximately one hour and 30 minutes. Peter Hodges’ and Julian Keable’s method is similar to Isler’s method and instead small manufactured concrete blocks as shims, wooden pallets, and a pit where their experimental tests were performed. Keable was able to perform his method in approximately 2 minutes. Scott Hussey-Pailos’s (2005) method uses a simple levering device to lift a block up course in one movement. This method was tested with materials of less strength than historical analogs (tested with materials weaker than those available in ancient Egypt), a factor of safety of 2, and lifted a 2500 pound block up one course in under a minute. This method is presented as a levering device to work complementary with Mark Lehner’s idea of a combined ramp and levering techniques.