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Background

Assembling pyramid proof A report on a special invited lecture presented by Dr RGH Parry, University of Cambridge, at the British Geotechnical Society annual general meeting, at ICE, London, on 17 June 1998. Reported by Tim Fitch, Paul Wiltcher & Scott Hu

The Great Pyramid was built as the tomb of the Pharaoh Khufu and thus it is known from his period of reign that the construction of the Pyramid took about 20 years. In order for the Pyramid to have been constructed during this period, the blocks would have to have been transported from the quarries, raised and positioned at an average rate of one every two minutes, with a peak rate of probably one a minute.

This construction rate could not have been achieved by using techniques such as sleds, levers, rockers and primitive cranes. Thus another method had to have been used and the use of contrivances made of short timbers is the most likely method.

Introduction

Dr Parry started the discussion with brief insight into the pyramids in general and some of the theories that have been documented over the years as to the construction techniques used in raising the stones into position on the pyramids. In this, he outlined the three major periods of Egyptian history, the Old Kingdom from 2650BC to 2140BC, the Middle Kingdom 2040BC to 1640BC and the New Kingdom 1550BC to 1070BC.

The seven major stone pyramids were built during a 150 year period of the Old Kingdom (the times between these periods are believed to be epochs of decay when political unity was destroyed). Nearly 100 pyramids were built in total, many of mud-brick, but only the major stone pyramids are of such a scale that they have attracted the attention of historians and millions of tourists over years.

Amazingly the ancient Egyptians did not consider the methods used in constructing the pyramids sufficiently unusual or important to be worth recording in either writing or illustration, and as a result their construction is still a source of great fascination today.

The Great Pyramid

The Great Pyramid, named so because it is the largest of the seven major pyramids, was the fifth to be built. It is 147m high and has a square base of 230m. It contains some 2.3M limestone blocks, each weighing between 1t and 7t and averaging 2.5t. The total mass of the pyramid is believed to be 6Mt, and it took approximately 20 years to build - a surprisingly quick period.

Quarrying, transportation and construction

Dr Parry said his interest in the pyramids has gone further than some earlier theories and considers how the limestone blocks had been transported from the quarries to the construction sites, as well as to the raising the stones. Topographical evidence in the area suggests that the quarries, which were the main source of the limestone blocks, were between 500m and 5km distant from the pyramids, and in some cases involved crossing the Nile.

These limestone quarries were kilometres in length and the production rate must have required hundreds of stones to be worked on simultaneously.

Over the years, Dr Parry said that numerous methods have been suggested as to how the blocks were 'lifted into position'. One of the most common suggestions was that the blocks were placed on sleds and then pulled on rollers which were continually placed in front of the sled.

However, Dr Parry explained that this method required too much effort to move the sled up ramps and the rollers were difficult to control. Consequently this approach would have been too labour intensive and time consuming for the time frame within which the pyramids were constructed. Thus another method must have been used, which according to earlier historians might have included the use of levers, rockers and primitive cranes.

The lever method involved the use of levers to lift the blocks up so that chucks could be placed underneath. Once raised sufficiently, the block is then pushed on to the next course. However, this method is not feasible since the act of pushing the blocks on to the next course would require the workforce to be levitated in mid air.

The Egyptians were thought by Petrie, the 'Father of Egyptology' to have used a cradle or rocker, models of which were found by Petrie in New Kindgom foundation deposits. Blocks were placed on a cradle which was rocked from side to side, during which timbers were placed beneath the cradle, thus raising the block. Dr Parry was of the opinion that the theory was flawed since the method would be too hazardous and time consuming.

Dr Parry reported that he believes an easier and more convincing description of how the pyramids were built is that told by the Greek Historian Herodotus in 450BC (about 2,000 years after the construction of the Pyramids). He refers to the stones being raised in tiers by 'contrivances made of short timbers'. These were probably the 'rockers' found by Petrie.

Dr Parry presented his theory of how the 'rockers' where used. He suggested that these wooden quarter circle shapes were applied to four sides of the blocks, to form a circle which could be rolled along, up and down slopes. These can be shown by simple theory of mechanics to be a highly efficient way to move heavy blocks. The arrangement was also easy to manoeuvre. When it needed to be turned, the block was rolled on to a central support and rotated horizontally.

This method would have been used for both transporting the blocks from the quarry sites and for raising and placing the blocks in the pyramid. According to Dr Parry, each block was approximately square in section and varied in depth from over 1m thick at the base to 0.6m thick at the top, and would have been rolled up ramps constructed up the sides of the advancing pyramid.

In the lower one-third height of the pyramid (making up two thirds of its volume) the ramps would have been on earthen fill placed at its angle of repose against the sides of the pyramid, but above this masonry ramps would probably have been used.

To prove how easily the blocks could be transported and then ramped up into position, Dr Parry carried out a scale model test during his talk. He demonstrated using two models, one with a slope of 1:10 and another slope of 1:4. On both he showed how much harder it was to pull a 5.5kg weight on a smooth low friction sledge, than attaching wooden quarter circles to the weight and rolling that up the slope. In the exercise, Dr Parry used cotton to take the place of the rope, which snapped while demonstrating the sledge method, proving his theory perfectly!!

To prove his hypothesis furthermore, Dr Parry described full scale tests of the method, carried out in Japan by Obayashi Corporation. In these tests, he demonstrated how a 2.5t weight could be pulled up a 1:4, 15m long slope by 18 men, with some considerable ease.

Dr Parry said it would not have been practicable to have constructed ramps with a slope less than 1:4. On a level surface, two or three men could push the block from behind at fast walking pace, which would have allowed rapid transport from the quarries to the site.

Further evidence of this being the likely method employed during the construction of the pyramids was the sand and rubble mound around the base of the partly collapsed Meidum pyramid (the second of the major stone pyramids). Dr Parry said that this was probably the remains of the ramps that were constructed around this pyramid, rather than - as is generally assumed - collapsed material from the pyramid, as this would have probably been removed from the site by later generations.

Dr Parry suggested that there were seven construction stages in building a major pyramid:

1. Quarrying and shaping

2.Load onto transport method

3.Transporting

4.Final dressing of stones

5.Raising the stones

6.Moving across the working platform and into position

7.Final positioning

One further outstanding engineering feat which Dr Parry said the Egyptians overcame was the construction of the haul roads from the quarries to the Pyramid. He noted that Herodotus claimed that these alone took 100,00 men, 10 years to construct, working three months of the year.

Discussion

The meeting was brought to a close with a short period of questions from the audience. These included:

Q: Was the compressive strength of the wooden 'segments' a governing factor in the transportation of the blocks?

A: No, the governing factor was more likely to be the bearing capacity of the haul road.

Q: If this method (the use of contrivances made of short timbers) was used, then surely we would expect to find the remains of thousands of small timbers around the base of the Pyramid?

A: Not really, since wood is a valuable commodity in the desert, any disregarded timber would have been salvaged for firewood or other uses.

Q: In your opinion, were the pyramids meant to represent heaven on earth, with the Nile symbolising the milky way and the Pyramids representing the main stars?

A: There is some evidence supporting this.

Dr Craig, chairman of the British Geotechnical Society then thanked Dr Parry for his lecture, and the informal discussion was brought to a close.

Dr Parry is secretary general of the International Society for Soil Mechanics & Geotechnical Engineering.

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