samedi 9 avril 2011

“Guizeh avant la Quatrième Dynastie” : une étude de Colin Reader sur l’âge du Sphinx - 2e partie

Colin Reader : 
Giza Before the Fourth Dynasty” - II


                      Première partie : ICI

The counter arguments
Schoch's context for the early Sphinx
As part of my research, I have considered Schoch's claim that the use of stone in building at Jericho and Nabta Playa provided a context for the early Sphinx which he proposes. With respect to the possibility of links with Jericho, Michael Baigent (in his book Ancient Traces (18)) links Predynastic pots found at Giza (...) to evidence of traders from the Jericho region who had settled in the Late 
 Predynastic town of Maadi, across the Nile valley from Giza (...). Baigent describes how many of the pottery remains encountered during the archaeological excavation at Maadi, were clearly influenced by Jericho - evidence, he concluded, that people from Jericho had settled in Maadi, bringing with them their knowledge of working masonry and (as he implies) building the Sphinx.
Whilst this link is intriguing, it cannot be substantiated by archaeological evidence from the Maadi site. An important publication on the subject is 'Maadi I - the pottery of the PreDynastic Settlement', (19) in which the authors discuss the presence of Palestinian (including Jericho) pots of Chalcolithic age (c. 4000-3000 BC). Not only is this date inconsistent with the pre-5000 BC date advocated by Schoch for the construction of the Sphinx, but the authors also note that the Palestinian pots were of a single type and represent only some 3% of the total assemblage. Given the rich variety of forms of Palestinian ware, the firm conclusion reached was that these pots were not imported in their own right, nor were they brought by settlers. Their presence in Egypt was evidence of trade in a limited range of commodities imported from Palestine. The Palestinian pots found at Maadi were simply the standard containers for these commodities.

Illustration empruntée à
As for Nabta Playa, well the Sphinx actually has very little in common with the stone circle discovered at this site in southern Egypt (dated to approximately 6000 BC). The scale of the two monuments could not be more different. The Sphinx, at over 70m long, contrasts starkly with the Nabta circle, which is only 4m in diameter. Unlike the Sphinx temple and Khafre valley temples (which West and Schoch also date to the same era as the Sphinx and which consist of carefully quarried worked and placed masonry) the Nabta circle is built from roughly hewn blocks. A number of large worked stones have been found buried in the sand at Nabta but, in spite of the fact that these monoliths show some advanced features of working in stone, they do not represent true masonry and cannot, therefore, be considered as comparable with the Sphinx and its associated structures.

Nabta Playa - cliché Raymbetz (Wikimédia commons)
In my view, these distant sites (Jericho and Nabta) fail to provide the early context for the Sphinx which Schoch has sought. More importantly, we do have archaeological evidence from Egypt for the period before 5000 BC. The capabilities of the cultures from this time are well established and clearly do not include the working of stone masonry.

The geophysical evidence reported by Schoch
Geophysics, provides an immensely useful range of non-destructive prospecting tools. However, it is quite common for one geophysical technique to show anomalies where no features in fact exist. In addition, different results can often be obtained by the same technique if additional factors come into play. Conclusions drawn from geophysical investigation should always, therefore, be confirmed by intrusive methods. No intrusive investigation has been undertaken within the Sphinx enclosure by Schoch.
An illustration of the vagaries of geophysical survey is provided by the team from Waseda University in Japan, (20) who used two advanced geophysical techniques within the Sphinx enclosure: (a) ground penetrating radar (GPR) and (b) microgravity techniques. In their first season, the team used GPR with a frequency of 150MHz and identified two potential cavities in front of the Sphinx. During their second season, however, the same techniques were used but with a reduced frequency of 80MHz. No significant anomalies were encountered at the appropriate locations on this occasion. Which set of geophysical data is to be believed ? As Yoshimura et al. candidly state: 'It was found that the existence of a cavity could not be confirmed without a boring operation'. However, in Schoch's opinion the seismic geophysical surveys undertaken by Thomas Dobecki and himself confirmed his pre-5000 BC date for the original construction of the Sphinx. (20)
In my opinion, it is necessary to question the validity of Schoch's key assumption - that the results of the seismic geophysics actually represent evidence for weathering rather than some other factor. Schoch's conclusion, that the seismic survey indicates anomalous shallow weathering at the rear of the Sphinx, is only one possible interpretation of the data - there are other equally valid interpretations.
In his original KMT article on the age of the Sphinx Schoch discusses four seismic lines within the Sphinx enclosure. (22) The line at the rear of the Sphinx (line S3) suggested a depth of weathered limestone in the order of 1.2m. Three further lines (S1, S2 and S4) to the north and south of the Sphinx (parallel to the body and in front of the paws) indicated weathered rock to a depth of 1.8 to 2.5m. However, the KMT article simplified the original seismic work, omitting any discussion of seismic line S9, which ran across the floor of the Sphinx temple. In their joint paper, Dobecki and Schoch reported that S9 indicated weathering to 1.2-1.5m depth. In addition, they state that the depth of weathering indicated by S4 (in front of the Sphinx) approached 4m, not the 2.5m stated by Schoch in KMT. If these depths are plotted on an east-west section through the Sphinx enclosure and Sphinx temple (bearing in mind that the floor of the Sphinx temple is cut three metres lower than the floor of the Sphinx enclosure) the 'weathered' depths can be connected by a sub-horizontal line which closely parallels the dip of the strata. Schoch's 'weathered zone', therefore, may be simply a function of the structure of the Member I rock - reflecting the bedding of the limestones beneath the Sphinx enclosure.

The geological case
Unsurprisingly, Schoch's conclusions regarding the geology and its implications for the age of the Sphinx were rejected by Egyptologists. Great effort was put into countering what was widely regarded as a 'heresy'. As well as Egyptologists revisiting the evidence for the 4th Dynasty attribution of the Sphinx (some of which I discussed at the beginning of this paper), a number of geologists who had experience of working in Egypt countered Schoch's interpretation of the processes of weathering and erosion responsible for the morphology of the limestones exposed at the Sphinx. The two principal geological arguments were those of James Harrell (23) and of K. L. Gauri. (24)
Harrell argued that the degradation of the limestones within the Sphinx enclosure could be attributed to the effects of accumulations of wet sand which would locally enhance chemical weathering of the limestone. The processes Harrell described to promote the wetting of accumulated sand within the Sphinx enclosure included the introduction of water by extreme Nile inundations into the lower lying sands. This moisture, Harrell then argued, rose by capillary action up to 2m into the overlying sand. Although in hot, arid areas capillary fringes are present above groundwater in bedrock, it has to be questioned whether such a deep capillary fringe would develop in a loose, coarse grained soil, such as accumulated sand.
Given the difficulties with Harrell’s theory, the wet-sand hypothesis has not been as widely supported as the conclusions reached by Gauri. For a number of years Gauri had been working with Mark Lehner on the nature of the limestones exposed by the excavation of the Sphinx. One particular objective of Gauri's work was to establish the geo-chemistry of the limestones, the masonry and the mortar which had been used in the various phases of restoration of the Sphinx. As part of this work Gauri was able to recover samples of the limestone and mortar and have detailed laboratory analysis undertaken. Gauri's precise work led to a system of reference for the bedded limestone which is employed widely today and is summarised in Figure 6.

Fig. 6: A geological section through the Sphinx and Sphinx enclosure,
showing the three limestone members.

Gauri established that the lowest strata, Member I, consists of a massive and durable limestone, exposed across much of the base of the Sphinx enclosure. The lowest lying parts of both the body of the Sphinx and the western exposures are Member I strata, with the quarried height increasing towards the north-west. The entire northern terrace of the enclosure consists of Member I limestones.
The upper body of the Sphinx and the upper part of the enclosure walls to the south and west, consist of the overlying Member II strata - a series of seven fine grained limestone units. Of these seven units, units 1 to 6 have been further divided into two sub-units, the lowest of which consists of a less durable, marly rock (with the upper sub-unit being coarser grained and generally more durable).
The head and neck of the Sphinx are carved from Member III rocks which have also been divided into two sub-units. The neck of the Sphinx consists of relatively less durable rocks, whereas, the head has been carved from 'one of the most durable limestones exposed at Giza'. The durability of the Member III strata has been cited by others to explain the remarkable preservation of the Sphinx's face and nemes head-dress.
Gauri attributed the degradation of the Sphinx enclosure primarily to the effects of a process which he refers to as 'chemical weathering and exfoliation' in which dew, forming at night on the exposed limestone, removes soluble salts from the surface of the rock. Capillary forces draw this solution into the pores of the limestone matrix, where further salts are dissolved from the internal pore walls. As daytime temperatures rise, the solution begins to evaporate, precipitating salt crystals within the confined neck of the pores. The pressure which the crystals exert as they grow, leads to flaking of thin rock layers from the surface of the limestone.
Gauri argued that this process had operated throughout much of the accepted history of the Sphinx and was continuing at present. As Gauri explains it, the effect of chemical weathering on the bedded limestones produced a 'vertical profile of the Sphinx and the walls of the Sphinx enclosure made of alternating projections and recessions'.
It is important to note here that the degradation described by Gauri, which results from the action of chemical weathering and exfoliation, is controlled by the bedded nature of the limestone, with the less durable units (those identified by the Roman numeral 'i') receding further from the cut face than the inter-bedded more durable strata. The process identified by Gauri therefore leads to the development of horizontal banding across the exposed limestones, as can be clearly seen on the body of the Sphinx (Figure 3).
The influence which the bedded nature of the rocks has had on the variation of the degradation - 
Fig.1 : cliquer pour agrandir
 particularly of the Member II rocks - is an important consideration. But, as Schoch has pointed out, this horizontal banding is not the only characteristic feature of degradation within the Sphinx enclosure. What Schoch does not appear to have identified, however, is that the 'coved' degradation - considered by him to be the result of erosion by rainfall - is not present to any significant extent on the body of the Sphinx or on the eastern end of the southern enclosure wall. The 'coved' appearance is present only on the western walls of the Sphinx enclosure - that is the western wall behind the Sphinx (Figure 4 & 5) and the western section of the southern enclosure wall below Khafre's causeway (Figure 1).
I do not dispute that the processes of chemical weathering and exfoliation described by Gauri were responsible for extensive weathering of the strata within the Sphinx enclosure - the banded appearance of the body of the Sphinx testifies to the role that these processes have played. However, it is clearly evident that the features of degradation are more intense in the west of the enclosure. This greater intensity can not only be identified by the 'coved' appearance of the degraded faces in the west but also, as Gauri's own publications show, (25) by the fact that the banded degradation of the western enclosure walls is deeper than in the east of the enclosure. As this greater intensity represents a variation along rather than across the exposed beds, it can be considered as independent of the bedding and cannot, therefore, be explained by Gauri's model.
My conclusion is, therefore, that to explain all the features of degradation within the Sphinx enclosure, other factors must be taken into account and that the degradational history of the Sphinx is more complex than Gauri suggests.

An alternative interpretation
With regard to the location of the Sphinx, the fact that the degradation of the Sphinx enclosure is more intense in the west and, moreover, is restricted to the walls of the enclosure is highly significant.
Although arid conditions dominated during the dynastic period of Egyptian history, wetter periods are known to have been experienced up until as late as the end of the 5th Dynasty (OC approximately 2350 BC). (26) pyramides. So, the rainy conditions of 5000 to 7000 BC, to which Schoch attributed the degradation of the Sphinx, were separated from the later arid conditions by a transitional phase which, between the Predynastic period and the end of the 5th Dynasty, was characterised by an increasingly arid climate interrupted by occasional, probably heavy, seasonal rains.

Google Earth (copie d'écran)
 The Giza necropolis sits on a gently sloping limestone plateau, which falls from its highest point in the west (beyond the pyramid of Khafre) for a distance of over one and a half kilometres before reaching the former limit of Nile inundation (a short distance east of the Sphinx). With limited vegetation or sub-soil cover, sporadic heavy rainfall would have quickly saturated the fine grained limestones which form the surface of the plateau. Any excess water, unable to infiltrate through the saturated surface, would have been shed downslope as run-off. Although these rain-storms would have been of short duration, the momentum gained by run-off across an extensive catchment (such as that at Giza) must have produced surface flows capable of significant erosion.
The presence of a small wadi to the north of the Sphinx (as already discussed above) suggests that the area originally lay within part of the natural drainage system of the Giza plateau. This natural drainage system may actually have been modified by the excavation of the Sphinx but the extent of any such modification cannot be assessed with any certainty. However, the important issue is that the eastward sloping topography of the site, together with the orientation of the Sphinx enclosure and any effect the excavation of the Sphinx may have had on the local surface hydrology, is likely to have led to the discharge of run-off into the west part of the Sphinx enclosure, eroding the limestone along the exposed western enclosure walls and selectively exploiting any joints exposed along the cut face.
This rainfall run-off model is fully consistent with the distribution of the degradation which is present within the Sphinx enclosure. Not only would rainfall run-off lead to more intense degradation in the western part of the Sphinx enclosure but the less intense degradation elsewhere is also explained. Comparatively little run-off will have discharged over the exposed faces in the east of the enclosure and the body of the Sphinx generated little run-off itself as it was isolated from the plateau by the surrounding excavation of the Sphinx enclosure.

(Wikimédia commons)
The influence of water at Giza
So, the more intense degradation of the western walls of the Sphinx enclosure can be readily explained by the erosive potential of rainfall run-off. However, although erosion by run-off appears to offer the most likely explanation for observed features, it is important to give consideration to other processes in order to establish whether the degradation of the Sphinx enclosure could, perhaps, be explained in some other way.
Having already identified the problems associated with the wet sand hypothesis, I considered if there were any means by which chemical weathering and exfoliation may have led to the pattern of degradation which could be observed. The effects of chemical weathering could be modified in three ways :
(1) By certain exposures being protected from degradation by, for example, accumulations of wind blown sand. Under such a scenario, unprotected areas would be more heavily degraded ;
(2) By variations in the intensity of chemical weathering itself, brought about by factors such as aspect (i.e. the orientation of an exposure with respect to the sun) ;
(3) By the effect of sand abrasion.
Given the dominant northerly wind direction and the easterly slope of the plateau, dry, windblown sand is most likely to start filling the Sphinx enclosure from the north and west, with the covering of windblown sand protecting the underlying exposures. The exposures which were the first to be covered with sand are therefore those in the west of the enclosure - which happen to be the most heavily degraded.
Aspect can greatly influence chemical weathering. Although the more intensely degraded western enclosure wall is exposed to direct sunlight throughout the morning, so too are the same limestone beds exposed across the 'chest' of the Sphinx. However, unlike the western enclosure wall, the east-facing 'chest' of the Sphinx does not exhibit the intense and characteristic 'coved' degradation. This evidence alone is sufficient to demonstrate that the more intense degradation in the western part of the Sphinx enclosure has not developed due to the aspect of the exposures.
As for the abrasive effect of windblown sand, movement of sand is controlled by a process known as saltation, in which individual grains of sand tend to 'bob' along the surface, only rarely getting carried at any significant height above ground level by the wind. Although, this process will affect exposures close to ground level, its effect on more elevated exposures is limited. The effect of sand abrasion within an excavation such as the Sphinx enclosure is also likely to have been limited. At an excavated site, airflow will lose much of its energy to turbulent flow in the wake of the lip of the excavation. This turbulent flow will cause any sand load to be dropped, rendering the erosive capacity of the sand negligible. The intense degradation located low down on the walls of the western Sphinx enclosure could not, therefore, be the result of abrasion by wind blown sand.
These considerations lead me to conclude that any mechanism which relied on chemical weathering and exfoliation, sand abrasion, aspect, the protective effect of accumulated sand (or any combination of these processes) to explain the distribution of degradation within the Sphinx enclosure, appears to become increasingly contrived and, as a result, increasingly untenable. Not only is erosion by run-off the most straightforward explanation for the observable features at Giza but there is abundant evidence for the effects of such erosion.
During his 1930's excavation at the site of Menkaure's valley temple (a few hundred metres south of the Sphinx), George Reisner found evidence that part of the temple had been extensively damaged by storm run-off. Reisner's interpretation of his finds was that, some time after Menkaure's death, a wall built from mudbrick at the western end of the temple was washed away by surface run-off which (he concluded) followed heavy rain.
Remarkably, within the Sphinx enclosure itself there is unquestionable evidence for erosion by running water, in the form of a shallow erosion channel that appears to issue from the base of the 'Main Fissure', at the point where it is exposed in the southern Sphinx enclosure wall (Figure 1). This shallow channel, identified by Mark Lehner, (27) cuts into the slightly sloping rocky floor of the enclosure and runs towards the rear of the Sphinx temple.

A pre-4th Dynasty Sphinx ?
Fig. 2
Of course, it is not necessary to question the attribution of the Sphinx to Khafre purely on the basis of the evidence presented above. Reisner's evidence for post-4th-Dynasty rainfall run-off at Menkaure's valley temple, together with the reconstructed climate of Egypt (with wetter conditions until the late 5th Dynasty), provide an opportunity for the western walls of a 4th Dynasty Sphinx enclosure to erode under the effects of rainfall run-off. So what reason is there to believe that the date of the Sphinx needs revision?
In a paper by Lehner entitled 'The Development of the Giza Necropolis: The Khufu Project', the development of Khufu's mortuary complex is modelled, with particular attention being paid to the temporary works (quarries, ramps, accommodation, etc.) which were a vital element of the construction programme. (28) 
Significant for the current discussion are two quarries, one of which is located to the west of the Sphinx and to the north of Khafre's causeway (Figure 2). The position of this quarry can be identified today by a depression in the surface of the plateau, filled with accumulations of wind blown sand (Figure 7).

Fig. 7: 'Khafre's causeway' with the depressions marking the 4th Dynasty quarries
on either side of the processional way.
Excavation at the eastern base of the quarry has identified a pair of closely spaced, parallel walls, built from rough masonry faced with clay. (29) These walls have a general north-south alignment and show a slight slope up towards the mastaba field to the east of Khufu's pyramid. Given their location and orientation, these walls have been interpreted by Lehner as part of a construction ramp used during the development of Khufu's mortuary complex. This date has been confirmed by mud seal impressions bearing the name of Khufu which were found in debris excavated from between the walls. This evidence securely dates the working of the quarry to the reign of Khufu.
The significance of a quarry at this location can not be overstated. From the earliest phase of Khufu's development, this quarrying will have disrupted the surface hydrology at Giza, with the open excavation intercepting any run-off from the higher plateau in the west and preventing its discharge towards the area of the Sphinx.
Although first worked during the reign of Khufu, Lehner has argued that the quarry was extended to the west during the reign of Khafre. As these additional areas of quarrying were opened up across the plateau, mud brick from construction ramps and large volumes of chippings from the working of masonry may have been deposited in the earlier, worked-out areas. It is not clear how quickly wind-blown sand then accumulated over this construction debris. However, the surface hydrology of the backfilled quarry will have been very different from that of the intact limestone plateau which preceded it.

Fig. 8:The rear of the Sphinx enclosure, with the sand-filled Khufu quarry (A)
beyond the modern low masonry wall.

Given the fine-grained nature of the limestones and the presence of relatively impermeable marly horizons within the Member II strata which originally formed the surface of the plateau, saturation is likely to have been achieved under comparatively moderate rainfall conditions. By contrast, the higher permeabilities of the unconsolidated windblown sand, within the abandoned quarries, will have required significantly more extreme rainfall conditions before the sub-surface reached saturation and run-off was generated.
Although rain is still a feature of the Egyptian climate, and heavy sporadic rains are experienced from time to time (heavy rain fell in Egypt, particularly around Luxor in late 1994), I consider that, since the climate became more arid at the end of the Old Kingdom, it is highly unlikely that any rainfall will have been of sufficient intensity to generate run-off from the backfilled quarry.
Interestingly, an aerial photograph of the Great Pyramid (apparently taken in the late 1920's during Junker's excavations at the site) shows quite clearly the effects of contemporary surface water run-off across the backfilled quarries. In the photograph, a number of drainage channels can be seen which, outside the quarried area (to the north and west), are relatively shallow. However, within the quarried area, run-off has cut deep channels into the back-fill material. This evidence indicates that run-off across the quarry west of the Sphinx would erode into the loose back-fill rather than run across the surface.
Khufu's quarries can therefore be seen to have had a significant effect on the surface hydrology of the Giza plateau. The conventional sequence of development, in which the excavation of the Sphinx took place after the construction of Khufu's pyramid, provides no opportunity for rainfall run-off to reach the Sphinx. Yet without the action of this agent of erosion it is not possible to fully account for all the features of degradation which are present within the Sphinx enclosure.
It is on this basis that I conclude that the excavation of the Sphinx was undertaken some time before Khufu's quarrying began, when rainfall over the more elevated areas of the Giza plateau was able to run off from a substantial catchment, gathering momentum before finally discharging into the Sphinx enclosure.

18. M. Baigent: Ancient Traces (London, 1998), p. 179.
19. I. Rizkana and J. Seeher: Ma'adi I - the Pottery of the Predynastic Settlement (1987).
20. S. Yoshimura et al.: 'Non-destructive Pyramid Investigation (1)' in Studies in Egyptian Culture 6 (Waseda University, 1987) and S. Yoshimura et al: 'Non-destructive Pyramid Investigation (2)' in Studies in Egyptian Culture 8 (Waseda University, 1988).
21. T. Dobecki and R. M. Schoch: 'Seismic Investigations in the Vicinity of the Great Sphinx of Giza, Egypt' in Geoarchaeology 7:6 (1992), pp. 527-44.
22. R. M. Schoch, op. cit [17], pp. 53-59 & pp. 66-70.
23. J. Harrell: “The Sphinx Controversy - Another Look at the Geological Evidence” in KMT 5:2 (1994), pp. 70-74.
24. K.L. Gauri: “Deterioration of the Stone of the Great Sphinx” in Newsletter of the American Research Center In Egypt 114 (1981), pp. 35-47; K. L. Gauri: “Geologic Study of the Sphinx” in Newsletter of the American Research Center In Egypt 127 (1984), pp. 24-43; Choudhory et al: 'Weathering of Limestone Beds at the Great Sphinx' in Environmental Geology and Water Science 15 (1990), pp. 217-23. K. L. Gauri et al. 'Geologic Weathering and its Implications on the Age of the Sphinx' in Geoarchaeology 10:2 (1995), pp. 119-33.
25. K. L. Gauri: “Geologic Study of the Sphinx” in Newsletter of the American Research Center In Egypt 127 (1984), pp. 24-43.
26. K. Butzer: Environment and Archaeology: An Ecological Approach to Prehistory (Chicago, 1971) '... extensive sheet washing - in the wake of sporadic but heavy and protracted rains - are indicated c. 4000-3000 BC. Historical and archaeological documents suggest that the desert wadi vegetation of northern and eastern Egypt was more abundant as late as 2350 BC, when the prevailing aridity was established.'
27. M. Lehner: 'Documentation of the Sphinx' in Proceedings of the First International Symposium on the Great Sphinx (Cairo, 1992).
28. M. Lehner, op. cit [7].
29. A. A. Saleh: 'Excavations around Mycerinus Pyramid Complex' in MDAIK 30 (1974), p. 137.

Troisième partie