dimanche 4 juin 2017

Une synthèse de connaissances ou hypothèses sur la construction des pyramides de l’Ancien Empire, proposée par une encyclopédie anglaise (1999)

L’Encyclopedia of the Archaeology of Ancient Egypt, éditée par Kathryn A. Bard, professeure d’archéologie, avec la collaboration de Steven Blake Shubert, publiée en 1999 par Routledge, peut être consultée ici dans son intégralité

Extraits (sauf illustrations) de cette encyclopédie, à partir de la page 778.

“The Old Kingdom Egyptians built pyramids for their kings and queens in a 72 km span of the Western Desert from Abu Roash to Meydum. Excluding the pyramids of Djedefre at Abu Roash and Seneferu at Meydum as outliers, the twenty-one other Old Kingdom pyramids are found in a 20 km stretch west of Memphis at Giza, Zawiyet el-Aryan, Abusir, Saqqara and Dahshur.
Egyptian pyramids are composed of a core comprising the bulk of the structure formed from limestone quarried nearby on the west bank, a fine outer casing of fine limestone quarried on the east bank (often called Tura after the site of one of the principal quarries), and backing stone between the core and the casing. When pyramids are formed of an inner step pyramid, packing stone fills in the steps or tiers.

Origin and development 

The first pyramid, Zoser's Step Pyramid, began as a mastaba, built with small, gray "one-man" limestone blocks (of a size that one man could carry) set along roughly horizontal courses in gravel and desert clay (tafia), and encased with fine white limestone. The builders twice expanded the mastaba before they conceived the idea of a pyramid, built in six steps from roughly shaped, larger core stones, directly over the fine Tura limestone casing of the earlier mastaba. They built the core as a series of accretions that lean inward about 74°, an effect achieved by tilting each course toward the core of the pyramid. This kind of core masonry is found in all later step pyramids : Sekhemkhet's ; the Zawiyet el-Aryan Layer Pyramid ; seven small "provincial" pyramids located at or near Abydos (Sinki), Elephantine, Edfu, Hierakonpolis (el-Kula), Nagada, Seila and Zawiyet el-Amwat (Hebenu) ; and the two step-pyramid building stages (E1 and E2) inside the Meydum pyramid.
The true pyramid was developed during the reign of Seneferu, who built the Meydum pyramid in seven steps and began to increase it to eight steps. Around the 15th year of his rule he founded a new pyramid necropolis at Dahshur, where he began what was intended as the first true pyramid at a steep slope of 60°. The builders still set core blocks at a tilt toward the center of the pyramid rather than on horizontal beds. As at Meydum, they built upon the desert gravel and clay, but here at Dahshur the softer surface soon threatened the steep pyramid with settling and collapse. They added a girdle around the base of the pyramid, reducing its slope to 54°31’13", but more settling and cracking prompted the builders to reduce the pyramid slope to 43°21’ at about half its height, creating the Bent Pyramid. At this point they began to lay core blocks along horizontal, rather than tilted, beds.
The Northern Stone Pyramid at Dahshur was built at a uniform 43° slope. A casing fragment that can only have belonged to the southeast corner was inscribed "bringing to earth... the fifteenth time of Counting", the 28th or 30th year of his reign. During his last years, Seneferu's builders filled out the steps of his Meydum pyramid with packing stones and Tura casing, laid on horizontal beds, to create a true pyramid (E3) of 51°50'35", practically the same slope as Khufu's pyramid and within the 52-53° range of the classic Old Kingdom pyramid. 
Photo de 1922
The gigantic stone pyramids, the classic pyramids of popular imagination, were built in only three generations. All other king's pyramids combined, including those of the Middle Kingdom (but excluding queens' and other satellite pyramids), contain only 54 percent of the total mass of the pyramids of Seneferu, his son Khufu and his grandson Khafre. The size of stone blocks and the quantity of gypsum mortar, as opposed to tafia, increased from the Dahshur to Giza pyramids. Khufu's was the largest and most accurately built and aligned of all Egyptian pyramids, rising more than 146 m from a base 230 m sq. and containing about 2.3 million blocks. Menkaure still used multi-toned stone blocks for his (the third) pyramid at Giza, but the total mass was less than that of Zoser's Step Pyramid.

The pyramid complex
With the exceptions of Seneferu and Khufu, who had some of their chambers moved up into the very body of the pyramid, Old Kingdom rulers had their burial chambers built or carved out of bedrock below the pyramid beyond a sloping entrance corridor which pointed generally toward the northern circumpolar stars. As the superstructure of the royal tomb, the pyramid was the central element in what Egyptologists call the "pyramid complex," a standard east-west axial layout that first appeared in simple form with Seneferu's Meydum pyramid : temple or chapel at the eastern base of the pyramid, causeway, and entrance or valley temple.
Since Khafre, pyramid temples included an entrance hall that connected to the causeway, a colonnaded court, five statue niches, magazines and an inner offering hall that, certainly from the end of the 4th Dynasty, included a "false door." Walls were decorated with painted relief carving. The causeway, often walled, roofed and covered inside with painted relief, ran down the plateau to the valley temple, the entrance to the complex. The valley temples were probably accessible by a canal or a channel that held water at least during the six-to eight-week inundation season, and possibly after the flood receded. The pyramid was surrounded by one or two walls of stone or mudbrick, forming enclosures that often included a small satellite pyramid. Nearby were often smaller pyramids for principal queens. Several pyramids are flanked by pits for the burial of boats, either real or stone-built imitations.

Pyramid building
Construction theories often assume a generic pyramid on a flat level surface. However, any account of how the pyramids were built must include the composition and setting specific to each pyramid. Building 5th and 6th Dynasty pyramids, or the Middle Kingdom pyramids with a mudbrick core, were very different tasks than composing the stone-block pyramids of the early Old Kingdom to which the questions and answers about pyramid building are most often addressed. The generations who built these pyramids developed and honed the necessary skills in masonry and labor organization selectively utilized by later pyramid builders.

Laying out the pyramid base 
Most of the Egyptian pyramids show a careful orientation to the cardinal directions. The sides of Khufu's pyramid, the largest (230 m to a side) and most accurately aligned, show an average deviation less than 4' of arc. Khufu's and Khafre's builders incorporated an irregular patch of natural bedrock protruding as high as 7-10m in the middle of the pyramid base. Khufu's builders did their finest leveling, off by only 2.5 cm in the entire circumference, on a platform built of fine limestone slabs. The baseline of the Khafre pyramid was simply a vertical cut in the foot of the bottom casing course of granite, where the slope of the pyramid would meet the top surface of the pavement of the pyramid court. These builders achieved their final results with a method of successive approximation, first drawing their lines on the sloping natural surface 7-10 m higher, then successively refining their squares as they quarried away the rock to the level of the final baseline. 
Illustration Franck Monnier, via Wikipedia 
The builders could have determined true north by marking the rising and setting positions of northern stars over an artificially leveled horizon, or by measuring the length and angle of the shadow of a vertical pole at the same time interval before and after noon.
Next, the north line had to be extended for the length of the pyramid base, without developing an increasing angle of error. During this operation, the ancient surveyors could have "checked in" to true north with a series of observation points along the line.
Extending the line great distances probably required pounding stakes in the ground. Lines of regularly spaced holes around the bases of the Khufu and Khafre pyramids may have been for staking an outside reference line, accurately marked by a taut cord from which the surveyors could establish the parallel lines of the pyramid base and its length using rods marked in cubits for incremental measurements.
Right-angled corners could have been established with the Pythagorean triangle, three of any unit on one side, four on the other and five on the hypotenuse (such triangles are found in the proportions of the Old Kingdom mortuary temples attached to pyramids) ; or the Egyptian set square, an A-shaped tool with perpendicular legs set at right angles and a cross brace ; or by pulling two intersecting arcs of the same radius from two different center points spaced along the same line. A line connecting the points of intersection will be at a right angle to the original line. Once again, the perpendicular line had to be extended without developing an increasing angle of error.

The core stone for the Zoser complex may have been quarried from a large trench or "moat" that surrounds the enclosure. At Dahshur and Abusir, quarries for core stone are located west of the pyramids. Most of the core limestone for the three Giza pyramids came from quarries along the low southeast part of the Mokkatam Formation, where thick layers that alternate soft-hard were advantageous for extracting large blocks. Farther south, the Ma'adi Formation's thin crumbly layers of clay and limestone provided material to build ramps. The broad wadi between the two plateaus probably served as a conduit for deliveries from outside Giza.
Casing stone was extracted from east bank quarries along terraces or banks in deep galleries that followed the best layers of stone, beginning with a "lead" shelf that would become the ceiling of the gallery. Granite was extracted from Aswan, either as natural boulders that were shaped into blocks, or quarried by means of separation channels pounded out with dolerite hammer stones.

Cutting stone
Modern Egyptian masons split very large blocks by simply etching a line with a corner of a heavy flat-headed hammer, then pounding the surface directly until the stone falls away to the desired cleavage. They also use the flat end of smaller hammers to dress the surface of a block by hitting it directly, which causes thin flakes to pop off the surface.
Ancient masons did the same, albeit with dolerite hammers of diverse sizes and forms, hand-held and hafted, as we know from fragments recovered in excavations. The diversity of Old Kingdom hammer stones has yet to be cataloged.
Metal for tools was limited to copper. Use of a metal point, or "nail" for rough work, is evidenced by long, thin and deep strokes in unfinished jobs such as the subterranean chamber underneath Khufu's pyramid. The chisels used for fine dressing masonry as extensive as the pyramid casings were all the width of a thumb or less, as evidenced by chisel marks on unpolished stone. Copper chisels needed to be sharpened and reworked often.
There are numerous saw marks and drill holes on hard stone such as granite and basalt at several pyramid sites. Copper blades and cylinders guided an abrasive wet slurry of quartz sand, which did the cutting, possibly mixed with gypsum. Some ancient cuts still retain a dried mixture of quartz sand and gypsum tinted green from the copper blade.

Rope, perhaps the most important tool in pyramid building, certainly of all block moving operations, had to be thick enough to withstand the strain of pulling multi-ton loads, yet thin enough that the haulers could get a good grip. About a dozen men could have tumbled blocks weighing two tons or more short horizontal distances by pulling on ropes tied around the top of the block while others pushed and levered from behind. Today's Egyptian quarrymen maneuver heavy blocks by tipping and turning them on a small hard fulcrum or pivot, such as a stone cobble. The ancient Egyptians used round dolerite balls like ball bearings to maneuver into position heavy sarcophagi in tombs at Giza.
Rollers, small cylindrical pieces of hard wood, could have been used for block moving, with the requirement that the underside of the load and the track must be smooth and hard. As few as ten men on two lines could pull a two-ton block up a grade that matched the lower parts of the pyramid construction ramps. To move blocks from the harbor or quarry to the pyramid exclusively by this method would have required an enormous supply of rollers, which were probably labor-intensive to produce in a country lacking the modern lathe and short on trees.
Wooden sleds and hard lubricated surfaces were most probably used for transporting blocks overland. Tomb scenes show funerary statues dragged on sleds, as a man pours water from a jar onto the surface just in front of the runners of the sled. Near the 12th Dynasty pyramids of Amenemhat I and Senusret I at el-Lisht, archaeologists have found hauling tracks composed of limestone chips, mortar and wooden beams spaced like railroad ties.
Pyramide d'Amenemhat Ier à Licht
Pyramid builders probably used ramps to raise most of the building material. Mudbrick ramps have been found near the Middle Kingdom pyramids of el-Lisht, including ramps that must have been used to raise stone up onto the pyramid of Senusret I. Construction ramps for the 4th Dynasty stone-block pyramids must have been large enough that we should expect to find sizable deposits of the material from which they were composed. At Giza, the quarries south of the pyramids are filled with millions of cubic meters of tafia, gypsum, and limestone chips. Remains of ancient ramps and construction embankments associated with structures other than pyramids at Giza are composed of such material.
Ideas about the form of pyramid construction ramps can be reduced to two major proposals : (1) a sloping straight ramp that ascends one face of the pyramid, and (2) one or more ramps that begin near the base and wrap around the pyramid as it rises during construction. Straight ramps have been found at the unfinished step pyramids at Sinki (South Abydos) and Saqqara (that of Sekhemkhet). Serious problems result in using a straight ramp for the higher reaches of the large 4th Dynasty pyramids. In order to maintain a low functional slope (e.g. about 1 unit of rise in 10 units of length), the straight-on ramp must be lengthened each time its height against the pyramid is increased. Either work stops during these enlargements, or the ramp is built in halves and one side serves for builder traffic while the ramp crew raises and lengthens the other half.
In order to maintain a functional slope up to the highest part of the pyramid, the ramp would need to be extremely long. At Giza, this slope would take the ramp for the Khufu pyramid far to the south beyond the quarry where Khufu's builders took most of the stone for the core of his pyramid.
The wrap-around ramp has been proposed in two major forms, either supported on the slope of the pyramid or supported on the ground and leaning against the faces of the pyramid like a giant envelope with a rising roadbed on top. Since it cloaks most of the pyramid, such a ramp makes it difficult to control the squareness and slope as the pyramid rises by checking back to the part already built. A ramp founded on the 52-53° sloping faces requires extra stock of stone on the casing blocks in wide enough steps to support it, a requirement that is not met by the unfinished granite casing on the lower part of the Menkaure pyramid. Near the top, the faces of the pyramid become too narrow to support any large ramp which would anyway become increasingly steep.
The form of the supply ramps probably changed as the pyramid rose. Near the base, the builders could have delivered stone over many short ramps. As the largest pyramids rose about 30 m above ground, it is plausible that a principal ramp ran to one corner and along one side, leaning against the pyramid and gaining rise with the run. To complete the top of the pyramid, very small ramps, or levers, could have been used on steps left on the pyramid faces. Once the top was complete, the masons could have trimmed away the steps.
It has been speculated that many or most of the stones were raised by using levers to "seesaw" a block upward, raising one side at a time and placing supports underneath, then raising and supporting the opposite side, for which stepped supporting platforms would have been needed. Except for the uppermost blocks, which become smaller, it is inconceivable that such lever-lifting was used on the stepped courses of the core stone or the undressed casing stone to lift most of the blocks. Lever-lifting requires the use of well-planed wood cribbage, or stacked supports, as the blocks are raised, vastly increasing the wood requirement.
Evidence of ancient levering indicates it was mostly used for side movements and final adjustments. It is possible that levering was the only means to raise the last few blocks of the highest courses, near the apex, once the builders had brought them as far as they could on ramps.

Setting stones, rise and run
When pyramid core masonry consists of stone blocks they are loosely set with considerable mortar and debris fill, even in the Khufu pyramid, which may have the most regular core. Casing stones, however, were custom cut one to another and placed with the finest joins ever seen in any masonry.
The builders probably began by setting the corner casing stones and several stones in between to establish the "lead lines" of the four sides of the pyramid. The stonecutters in the work yard had only dressed one side - which would be the bottom - of each casing block. At or near their final places, adjacent casing blocks had their joining sides cut to fit before they were set down off rollers, wedges or other supports. The "flat-bedding" of each stone had to wait until its join face had been custom cut to fit with the next stone down the line of each course. The masons left a good amount of extra rough stone protruding on the front face of each block. As they joined one block to another, the masons drew on each block the lines where the sloping plane of the pyramid face intersected the extra stock. Then they chamfered or beveled the extra stock of stone on the outer face away from the pyramid facial lines. This beveling was a lead, created block by block, for the final dressing of the pyramid casing, starting from the top and working down to the baseline as they removed the construction ramps and embankments. As the masons cut away the extra stock to free the four faces, the beveled spaces between the blocks would come together. When the spaces between adjacent blocks closed to a fine join, the masons knew that they should not cut any deeper. They were at the desired plane of the pyramid face.
To avoid twist as the pyramid rose, the builders could have used wooden poles down on the ground as back sights aligned with the center axes and diagonals. In the rock floor around the large Giza pyramids, there are holes and notches that appear to align with the major lines of the pyramids. These have yet to be mapped.
Pyramide de Meidoum
Inner step pyramid
If the core masonry was built ahead of the fine outer casing, perhaps as a rough inner step pyramid, the masons could have transferred reference points and lines from the ground up onto the core for measuring out to the facial lines of the pyramid.
The Meydum pyramid has an inner step pyramid because it was first planned as such.
The steps of the inner seven- (E1) or eight-step pyramid (E3) have fine sharp corners and faces that could have served as references for measuring set amounts out to the slope of the enlarged true pyramid. We do not know if the largest pyramids of the 4th Dynasty were built with an inner step pyramid. The cores of Menkaure's pyramid and of the pyramids of his queens and Khufu's queens are composed of great rectangular blocks of crude masonry which must have been built ahead of the casing. On the southernmost pyramid of Khufu's queens (GI-c), there are small holes, about 5 cm in diameter, near the corners of the tiers of the inner three-step pyramid. Some of these align with the casing corners near the base. The holes might have held wooden pegs that carried temporary reference lines in cord for measuring out to mark the line of the outer pyramid face in the casing blocks.

Middle to late Old Kingdom
Pyramid building changed radically following the Giza group. The last pharaoh of the 4th Dynasty, Shepseskaf, built a large mastaba at South Saqqara, composed of large blocks like those in the Giza pyramids. Kings of the 5th and 6th Dynasties built classic "Meydum-type" complexes, but with smaller pyramids composed of clay, rubble and smaller stones. Weserkaf, the first king of the 5th Dynasty, built a pyramid only one-thirtieth the volume of Khufu's pyramid. The core of debris and small stones may reflect the thin geological layering of the Saqqara Formation. The core of Sahure's pyramid was built of five or six steps of mud mortar and broken stone with a wide "construction gap" in the center north side that allowed the builders to work on the inner corridor and chamber while they proceeded to raise the pyramid core. Such gaps, later filled, may have been used to build internal chambers and passages for earlier pyramids such as Khufu's, where the gap might be masked by backing stones. Neferirkare built a six-tier step pyramid of well-laid, locally quarried limestone retaining walls. A single course of red granite casing was laid but never smoothed.
The cores of the 5th Dynasty pyramids are often illustrated, following Richard Lepsius and Ludwig Borchardt, as stepped accretions around a tall and narrow central tower, like pyramids of the 3rd Dynasty, but without the inward tilted beds. However, when the Czech Abusir Mission excavated the unfinished pyramid of Reneferef in the 1980s, they found no accretions in the single completed step, only an outer retaining wall of four or five courses of well-laid gray limestone blocks and an inner line of smaller blocks that framed the trench of the burial chamber and construction gap. The fill between the two frames consisted of poor quality limestone, mortar and sand.
Although his reign was triple those of his longest reigning predecessors, Pepi II’s pyramid, the last of the Old Kingdom, was no larger than 150 cubits (78.60 m) square, 100 cubits (52.50 m) high, with a slope of 53°13', the 6th Dynasty standard. The five-step core was formed by retaining walls of small irregular stones bonded in tafia and Nile alluvial mud, then encased with heavy blocks of Tura limestone set without mortar. The retaining walls of the core are reminiscent of retaining walls in construction ramps and embankments at Giza. In effect, the descendants of the Giza builders dispensed with heavy stone blocks and simply built the pyramid core with the material, far easier to mold and manipulate, from which their predecessors formed temporary ramps.
As the pyramid core decreased in size and quality, the fine craftsmanship, complexity and standardization of the temples was increased. The German excavators estimated Sahure's complex was adorned originally with 10,000 m² of painted fine relief. The highly standard pyramid temple of the 6th Dynasty included more extensive magazines than early Old Kingdom temples, a clear separation by means of a transverse hallway between an outer temple (entrance hall, court, magazines) and inner temple (five-statue niche, single-pillar antechamber, offering hall). The pyramid interior, consisting of a standard three-part magazine, antechamber and burial chamber, included, since Unas, Pyramid Texts for the royal afterlife. The decrease in pyramid size and durability probably reflects a decrease in social and political centralization during the half-millennium of the Old Kingdom.