vendredi 19 août 2011

Nouvelles considérations sur les techniques de construction des anciennes pyramides égyptiennes, par le Professeur Frank Müller-Römer - II

Archaeological features of the Old Kingdom pyramids
Photo Marc Chartier
“Initially started as a mastaba, the Pyramid of Djoser was built in layers (two to each step), and is therefore rightly referred to as Layer Pyramid. The basic techniques for the construction of such Layer Pyramids were developed at that time. Blocks were arranged around the core, with inward-leaning layers. The pyramids of king Sekhemkhet and Khaba (?), of which only the stumps are preserved, and the small pyramids (possibly of Huni ?) were built according to this principle. There is practically no evidence for a smoothed casing here. (34)
The first Pyramid of Seneferu at Meidum was built as a Layer Pyramid in several stages. In stage E1 and E2, limestone blocks were used for the visible surface of the steps, and dressed after application. After the finishing of the Layer Pyramid in stage E2, the steps were filled with another layer (E3), so that the façade now formed a constant slope, rather than a stepped outline. Afterwards, it was cased with finely grained limestone. In this monument, we are able to witness the transition from a visibly stepped Layer Pyramid to a pyramid with steps filled to form a facade with a constant slope (‘true pyramid’). This development took place parallel to the construction of the Bent Pyramid. The cult pyramid of Meidum was also built as a Layer Pyramid.

It is virtually impossible to offer an archaeologically sound explanation for the construction process of the Bent Pyramid, especially its inward structures. The start of its construction is usually dated to twelve to fifteen years after the start of the construction of the Meidum pyramid, and at this time, no severe difficulties had occurred with the Layer Pyramid style. It is therefore likely that the Bent Pyramid was initially designed as a Layer Pyramid as well.
When the first stage of construction was completed, backing and casing blocks were added in the next stage to form a constant slope in its lower half. When the additional casing had been finished, the pyramid’s construction was continued from a height of 90 cubits (47m) onwards with a less steep slope. Moreover, the construction technique was modified : the stone courses underneath the casing were then set horizontally, that is to say the degree of inward leaning was lessened as the building gained height. Also, the stone blocks used were smaller than those used in the casing below.
The design of the attached Satellite Pyramid then followed the ‘new’, modified construction principle with horizontal courses of stone blocks. This might have served as a test for the construction technique later adopted in other pyramids.

To sum up, the transition from the principle of inward-leaning layers, as seen in the Layer Pyramids, to construction by means of horizontal courses, the latter being characteristic for the Fourth Dynasty, probably took place during the reign of Seneferu. Having been pinned down to the building process of the upper half of the Bent Pyramid, the attached cult pyramid, and the Red Pyramid, it can be explained from the difficulties that occurred during construction of the Bent Pyramid.

The Red Pyramid is the first to display fully horizontal courses of casing blocks. Due to its good state of preservation, archaeologists have not been able to obtain any definite information as to the structure of its core. However, it is hard to imagine that the core would consist of inward-leaning layers after the disturbing experiences made during the building of the Bent Pyramid.
Another significant change took place during the construction of the Red Pyramid, because the large blocks familiar from the Giza pyramids are used here for the first time. Consequently, new transport techniques must have been developed for these blocks. Considering the chronology of Seneferu’s reign, the pyramid’s construction started relatively late, and it is possible that the builders were pressed for time, so that changes in the construction technique were at least partly dictated by tight schedules.
It is not a far-fetched thought that the first and foremost way of improving construction techniques to such a degree as to enable the building of the Great Pyramids was to collect solutions developed from difficulties encountered previously in this epoch characterized by intense pyramid building activity. Therefore, we may conclude that the Red Pyramid consists of steps with horizontal courses, marking the beginning of the Step Pyramid style.
Scholars generally speak of a transition from the so-called Step Pyramids (as the Layer Pyramids are often mistakenly called) towards the ‘true’ pyramid during the reign of Seneferu. However, the actual circumstances of this transition are hardly ever considered. Within eighty years after the erection of the first pyramid by Djoser, the ‘classic’ pyramid was developed as the type of royal burial that should dominate the ancient Egyptian necropolis throughout the upcoming centuries. Seen from an evolutionary perspective, the development of Egyptian burial structures first started from the mud brick mastaba, moving on to the Layer Pyramid and the Step Pyramid and reaching a climax in the ‘classic’ pyramid with a constant slope.
Observations made on the breach in the South face of the pyramid of Khufu and in the tomb robbers’ tunnel on the North side, and also on the breach in the North face of the pyramid of Menkaure (fig. 11) suggest that the horizontal courses of the casing do not match those of the core. In both pyramids the filling within the core walls that form the steps consists of roughly hewn stones of various sizes and shapes piled on top of each other irregularly, and joined by mortar. Some of these are clearly unworked quarry stones.

Fig. 11 Cross-section (S-N) of the pyramid of Menkaure with steps archaeologically attested in the breach on the North face (drawn lines) and the other steps of the core reconstructed by analogy (dotted lines)

Production, transport and laying of the stones for the core would have required less effort than for the casing. The stepped core served to improve the inner stability of the building, while also increasing its resilience against external damage. However, the actual structure of the core of the Khephren pyramid remains unknown up until today.
Exact positioning and measuring of the casing’s base was essential. This was the only way to ensure that the sides would actually converge at the top. After each measurement, any necessary fine tuning could be executed in the following layer. The remarkable degree of exactness that was reached in the measurement of the base of the pyramid of Khufu – even while the rock spur in its middle would have precluded diagonal measuring – shows that measuring of this sort would not have posed insurmountable difficulties.
Any distortion of the pyramid was prevented by measuring the length of the sides of a finished course of casing blocks at the pyramid stump from one corner stone to the other (“length measurement”) and control of the horizontal course (“horizontal leveling”). Furthermore, straight lines were established between the corner stones which had been prefabricated to have a rectangular base and a defined slope of the outer ridge, indicated by marks on the upper surface of the blocks. (35)

Photo Marc Chartier
There is no sufficient evidence for orientation on the points of the compass for this purpose during construction of the pyramids, and with a view to other well documented measurement procedures, it does not seem probable either.
The so-called distortion observed by Petrie at the top of the pyramid of Khephren which is quoted by Unterberger as support for his hypothesis that the points of the compass were used during construction does not seem cogent upon closer examination.
While working at a considerable distance, Petrie measured the deviation of the lower preserved layers of casing in the upper part of the pyramid of Khephren from the directions of the pyramid’s base as follows : NE corner + 1.7 inch, SE corner + 0.6 inch, SW corner +0.3 inch, NW corner + 0.3 inch. Consequently, he arrived at an average of + 00°01'40'' of distortion inbetween the four sides. However, this argument is not effective, because such differences are more likely to suggest that minimal inaccuracies in the production of the corner stones. Rather, it is a remarkable achievement that there are only such minuscule irregularities from the ideal measurements. This is yet another proof for the astonishing degree of advancement of construction techniques in the Old Kingdom.
The foundations of the casing were leveled out and measured permanently. The same is true for the other courses of the casing and their respective offset. It was essential to maintain the same height of the steps in order to achieve a constant batter. Depending on the quarrying, the stone layers may have had different heights. Under such circumstances, exact monitoring of the batter was the only viable way to check the angle of inclination, on which the height of the pyramid depended. The fact that the pyramids’ exact slopes vary is most likely a result of different designs, or else just slightly inexact measuring. Besides, it has to be admitted that today, the angle of inclination can often be only roughly determined due to the pyramid’s state of preservation. It seems likely, however, that the actual height of the pyramid was not included in the initial design, rather, in effect, it resulted from the added offset of all steps.
The Step Pyramid style was kept in use throughout the Fifth and Sixth Dynasties, as is attested by archaeological findings on all pyramids of this period, including the cult pyramids and Queens’ Pyramids. The pyramids of Menkaure and Userkaf mark the beginning of a period of pyramids with less monumental dimensions than those of the Fourth Dynasty. The development continued in this direction until the end of the Sixth Dynasty (Pepi II). However, the technique used in constructing the steps changed during the Fifth and Sixth Dynasty. The stepped core walls of the steps consist of an outer wall executed in well-hewn stones with slight batter, while towards the inside, we find a filling of blocks of various shapes and sizes that are only roughly hewn and mixed with mortar and rubble. Thus, by using smaller blocks, it was possible to lower the expenses for production and transport in comparison to the pyramids of the Fourth Dynasty.
The courses of large well-hewn stones casing blocks characteristic of the Fourth Dynasty pyramids disappear, making way for smaller backing stones of irregular shape filling the spaces between the steps and the outer limestone casing. As a result, when the casing was stripped, the mortar was exposed to the elements so that parts of the core masonry collapsed. Stadelmann, Lehner and others speak of slack workmanship here ; similarly, Maragioglio and Rinaldi attribute the state of the building to the inferior quality of the masonry. However, I should like to argue that this construction technique was the result of experiences made in pyramid building to the extent that in smaller pyramids, a stable outer casing would have sufficed to protect the core from weathering or erosion. Surely, experience in pyramid building would have become increasingly profound over the years. Moreover, in order to keep within tight building schedules while also minimizing the costs, the small pyramids did not receive such a closely-fitted casing as the pyramids of the Fourth Dynasty, whose inner casing masonry even resists the weather and most of the erosion when much of the outer casing is stripped.
To sum up, all pyramids of the Old Kingdom, or at least from the pyramid of Khufu onwards, have stepped cores (layered or stepped construction). (36)
In the immediate surroundings of the pyramids, no ramps have been attested by archaeological evidence that could have been used for building the pyramid itself rather than for transport of stone blocks to the construction area. The pyramid of Seneferu in Meidum is the one notable exception to this rule.
The pyramids of the Old Kingdom were planned and built over a period of roughly four hundred years, and a broad spectrum of construction techniques must have been invented and applied, while the techniques themselves were improved continually.

Some previous explanations of pyramid building

Nearly all relevant explanations of pyramid construction have been formulated with respect to
the pyramid of Khufu. As stated above, with a view to archaeological evidence, the techniques did not change much throughout the period of four hundred years (Third to Sixth Dynasty), during which roughly twenty-five pyramids were built, with the one notable exception of the transition from Layer to Step Pyramid during the reign of Seneferu. Other improvements were introduced in a less dramatic way and can hardly be traced nowadays.

Therefore, we have good reason to assume that any theories on the building of the pyramid of Khufu should also serve to explain the building of other pyramids of the Old Kingdom.
An analysis of the suggestions published so far with reference to the building of the ancient pyramids in general, and the pyramid of Khufu in particular, yields the following three categories :
– solutions involving perpendicular ramps ;
– solutions involving ramps built along the pyramid’s sides ;
– solutions making use of lifting or towing devices.
Any discussion of the subject should fulfil the prerequisites listed above, for otherwise it does not measure up to the requirements of the situation, thus failing to meet the standards of academic discussion.

Photo de Félix Bonfils (1875)
Perpendicular ramps as suggested by Arnold (37), Stadelmann (38), Lauer (39), Lattermann (40) and others can be excluded as a means of construction on the grounds of the following
observations :
– the ramps require continuous increase in height and accordingly, width. This leads to regular disruption of the construction works, or at least considerable delays ;
– the ramps have a maximum slope higher than 7° respective 15° ;
– the volume of the ramps would have been enormous, easily reaching or even exceeding the volume of the pyramid itself, depending on the design of the ramp ;
– no archaeological evidence has been offered that cogently proves the existence of ramps or appropriately large rubble deposits ;
– free-standing ramps built from clay or mud bricks sustain their own weight only up to a height of 120 m. ;
– archaeological evidence from the Step Pyramids, notably the pyramid of Menkaure, contradicts the hypothesis that the core was erected layer-wise, casting doubts on an idea that is crucial to the ramp models ;
– due to safety concerns and aspects of construction technique, the application of the casing and dressing required scaffolding or other attachments to the pyramid’s facade.

Spiral ramps, as proposed by Goyon (41), Lehner (42), Klemm and Klemm (43), Houdin (44) and others can also be excluded as a method of construction on the grounds of the following observations :
– at the corners of the pyramid, spirals ramps would have necessitated transport of building material at an angle of 90°, even if the corners were chamfered. This was hardly possible, and even if it was, it would have been an excessively time-consuming task. Also, no feasible solutions have been offered as to the redirection of the traction force ;
– the idea that the core masonry was laid layer-wise is not corroborated by archaeological evidence ;
– the limited transport capacity of the spiral ramp leads to a schedule for the pyramids’ construction that by far exceeds the attested time frame ;
– as stated above with reference to other ramp models, due to safety concerns and aspects of construction technique, the application of the casing and dressing required scaffolding or other attachments to the pyramid’s facade ;
– exact measuring throughout the building process would have been difficult as spiral ramps are thought to have enclosed the pyramid, partly obscuring its outer face and corners. It would have been very difficult indeed to ensure a constant batter.
Furthermore, the authors suggesting ramps often omit calculations of transport capacities, thus
failing to set their solution in relation to the time frame suggested by archaeological evidence, which in the case of the pyramid of Khufu is a maximum of twenty-three years total.
The solutions offered by Arnold (45), Isler (46) and Graefe (47) who propose constructions involving steps leaning against the pyramid’s faces at right angles, are no more convincing. These models pose static problems because the steep slope would have required upward leverage of the stone blocks, which was practically impossible.
Several hypotheses about pyramid building (Graefe, Landt (48), Hölscher) share the idea that from the stepped core of the pyramids, which is archaeologically attested, it can be deduced that ramps were used which ran in line with the steps’ lateral surfaces, and whose slope was adjusted to the transport method chosen for the respective material. On the broad lower steps, several ramps could be installed on all sides of the pyramid, so that even the vast amount of material needed for the lower area of the pyramid could be transported and laid within an economical frame of time and effort. Keyssner suggests that stepped construction platforms were attached to the sides of the pyramid, with winches positioned on the steps to enable hauling up of the stone blocks. (49) Again, we must hold against this that the concept of layerwise building of the core employed in this model is not corroborated by archaeological evidence which rather suggests a stepped core.
Most hypotheses start from the assumption that traction force was employed, which is to say, bull carriages or workmen were used for hauling. If the loads were heavier than usual, or the ramp slopes steeper, larger carriages or more workmen would have been required, and also
increasingly long ramps.
Some suggestions concerning the transport of building material for the pyramids are based on
rather complex construction processes, so that one may wonder whether the ancient Egyptian
architects would have indeed employed such sophisticated methods. What is more, the issues of constructing the top of the pyramid, setting the pyramidion, casing, and dressing often suffer neglect. The same applies to safety concerns. From all this, we cannot but draw the conclusion that yet another construction method was used which neither involved perpendicular, nor spiral ramps, nor quite so large quantities of material, nor a step construction.

My suggestion, which I shall outline in the following chapter, combines the idea of ramps set out parallel to the pyramid’s sides and that of hauling devices with winches in connection with ramps with a steeper slope. Again, I should like to emphasize that I have incorporated only such techniques and procedures which are either supported directly by archaeological evidence or conclusions drawn from archaeological data.

à suivre : troisième partie

(34) The casing of the lowest step of the small pyramid at Saujet el-Meitin is an exception to this rule.
(35) Müller-Römer, F. 2011. Der Bau der Pyramiden im Alten Ägypten. Utz, Munich, 112.
(36) In the case of the Bent Pyramid, the Red Pyramid, and the Pyramid of Khephren, this has not previously been proven.
(37) Arnold, D. 1981. “Überlegungen zum Problem des Pyramidenbaus.” In MDAIK 37, 15-28.
(38) Stadelmann 1990, 266-275.
(39) Lauer, J.-P. 1989. “Le Problème de la Construction de la Grande Pyramide.” In RdE 40, 91-111.
(40) Lattermann, W. 2002. Der Bau der Cheopspyramide. München.
(41) Goyon, G. 1990. Die Cheopspyramide. Augsburg.
(42) Lehner, M: 1985. “The Development of the Gisa Necropolis: The Khufu Project.” In MDAIK 1985, 109-143.
(43) Klemm, R. and D. Klemm 1998. “Die Integralrampe als Konstruktionselement großer Pyramiden.” In H. Guksch, ed., Stationen. Beiträge zur Kulturgeschichte Ägyptens. R. Stadelmann gewidmet. Mainz: von Zabern, 87-94.
(44) Houdin, J.-P. 2007. Cheops. Die Geheimnisse um den Bauprozess der Großen Pyramide. Mainz: von Zabern.
(45) Arnold, D. 1981. “Überlegungen zum Problem des Pyramidenbaus.” In MDAIK 37, 15-28.
(46) Isler, M. 1985. “On Pyramid Building,” JARCE 22, 129-142, and Isler, M. 1987. “On Pyramid Building II,” JARCE 24, 95-112.
(47) Graefe, E. Über die Determinanten des Pyramidenbaus bzw. Wie haben die Alten Ägypter die Pyramiden erbaut ? at
(48) Landt, E. 1923. Ein neuer Kampf um die Cheopspyramide. Berlin: Weidmann.
(49) Keyssner, H.K. 2007. Baustelle Giza. Kritische Untersuchung zum Bau der Cheopspyramide. Karlsruhe : Institut für Baugeschichte der Universität Karlsruhe.