Egypt Feature Story The Pyramid of Khufu at Giza in Egypt
The Pyramid Proper, Part I: Core and Casing
by Jimmy Dunn writing as Alan Winston
The Great Pyramid of Khufu, for some 43 centuries, was ranked as the tallest manmade structure on earth, only being surpassed in height in the nineteenth century AD. To give a relative idea of its size, consider that the area covered by the Great pyramid could accommodate St Peter's in Rome, the cathedrals of Florence and Milan, and Westminster and St Paul's in London combined.
Khufu probably abandoned the royal necropolis at Dahshur because it lacked enough space to build the large complex he intended for his burial, and because there was not enough limestone nearby, but he may have also been concerned with the stability of the subsoil, which consists of slaty clay. He choose instead to build his pyramid on a rocky outcropping in the desert near modern Giza, where the subsoil was much more stable and there was also an abundant supply of high-quality limestone.
Like a few other pyramids, the structure was built over a rock jutting up in the middle, which made the pyramid core easier to construct and at the same time, strengthened it. Otherwise, the outcropping was reduced to a horizontal surface that was level to within just 2.1 cm (under one inch). Because of its greater precision, Borchardt thought that the east side was probably the baseline used for the foundation measurements.
The materials used in the construction of the pyramid came from quarries southeast of the pyramid. The limestone blocks were almost certainly transported over a ramp to the construction site. According to Lauer, the pyramid was then probably erected by means of a whole system of ramps, including the fifty meter wide main ramp that led from the quarries to the construction site. It is very possible that other, smaller ramps ultimately became a part of the pyramid's core. Of course, there are other theories regarding the structure's construction, with new ones seeming to crop up ever year. However, somewhat recently, remnants of ramps have been found by Dr. Zahi Hawass on the south side of the pyramid that attest that some type of ramping was indeed used.
This simple, effective method made it possible to elevate, over a surface of about five hectares, blocks weighing from three tons (at the lower levels) to one ton (at the upper levels). However, some blocks were even heavier. As an example, the construction of the king's chamber employed pink granite blocks weighing forty to sixty tons, and the granite beams that roof the King's Chamber and the stress-relieving chambers above it have been estimated to weigh from fifty to eighty tons. These all had to be raised to a height of about seventy meters.
Borchardt agreed with Lepsius' view that the core masonry was arranged in inclined accretion layers. However, recent investigations made by French geophysicists have shown that the structure of the core is extremely heterogeneous. It probably also contains compartments filled with sand, probably small rubble and other waste material, which would not only have saved considerable time, but would have diverted the pressure inside the pyramid more effectively than did solid masonry. This must have also been helpful during the occasional earthquakes that occur in Egypt. However, the dimensions and arrangements within the core of these compartments cannot at this point be precisely determined. These and other factors explain why recent estimates by some scholars reduce the number of estimated blocks in the pyramid from about 2.3 million down to about half of that, which of course have considerable impact on the time and labor required to complete the structure.
However, the outside walls of the core are indeed built with huge blocks laid in horizontal rows. Today, only 203 blocks remain. Those in the upper seven rows seem to have been broken off. The height of the blocks varies between about one and one and a half meters. As in the case of the earlier Red Pyramid, the slightly concave walls were intended to increase the stability of the pyramid's mantle.
Between the core and mantel, another layer of smaller stones was bound with mortar, which increased the cohesion of the two materials and the two masonry structures. In archaeological terminology, this intermediate layer is known as the "backing stones".
The casing which made the outer surface of the pyramid smooth was made of large blocks of fine white limestone, traditionally thought to have been harvested from the Muqattam range on the east bank of the Nile. Some, but very little of it is still in place, mostly at the base. These stones may weigh as much as fifteen tons. Recently, some scholars have conjectured that these stones could have come from the closer and more accessible quarries west of Djedefre's pyramid in Abu Rawash, where valuable, high-quality, brilliantly white limestone is also found.
Originally, the pyramid was capped by a pyramid shaped stone referred to as a pyramidion. Khufu's Pyramidion may have been covered in electrum, a shiny metal of gold and silver. However, this pyramidion is now lost, and may never be recovered, although not so long ago Dr. Hawass did find the pyramidion of the nearby cult pyramid.
With the pyramidion in place, the pyramid is thought to have rose some 146.59 meters (481 feet) originally, with a slope of 51o 50' 40". Over the years, it has lost about 10 meters (30 feet) from its top. Its base length is calculated as 230.33 meters (756 feet), with the greatest difference in the length of the sides being 4.4 cm (1 3/3 inch). The structure is square at all levels. It's orientation is to each of the cardinal points, though there is an error of 3' 6" off true north.
See Also
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The Pyramid of Khufu at Giza in Egypt: The Pyramid Proper, Part I: Core and Casing
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The Pyramid of Khufu at Giza in Egypt, The Pyramid Proper, Part II: Internal and Substructure
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The Pyramid of Khufu at Giza in Egypt: Other Standard Pyramid Elements
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The Pyramid of Khufu at Giza in Egypt: Khufu's Boats and Boat Pits
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The Pyramid of Khufu at Giza in Egypt: The Three Queen's Pyramids
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