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Egyptian Pyramids - Construction

The Egyptian pyramids are large, quadrangular, and hollow, having a broad base, contracting gradually towards the top, sometimes terminating in a point, sometimes in a plane surface, and built of large blocks of red or syenitic granite, or of hard calcareous stone. The four sides are so placed as to face the four cardinal points, and two of them are usually larger than the other two. Investigations conducted with a view of determining the character of these structures make it appear that they date from the period of the third dynasty to the twelfth (say 2500-2000 BC), after which none were built.

Each pyramid was commenced over a sepulchral chamber excavated in the rock, and the work went on during the lifetime of the king for whom it was intended. A low narrow passage was kept open as the tiers of stone were added, in order that access might be obtained to the central chamber from without; and when the monarch died the work ceased, and the last layers were then finished off and the passage closed up. The angles formed by the recession of each superior layer were filled up with small stones and bevelled off, so as to give a smooth sloping surface to the sides. The stones used varied in thickness from 2 feet to 4 feet, and the mechanical skill requisite to quarry these and to raise them to such great heights and adjust them in their proper places continues a matter of universal astonishment.

It is certain that the pyramids were each begun with a definite design of their size and arrangement; at least this is plainly seen in the two largest, where continuous accretion (such as Lepsius and his followers propound) would be most likely to be met with. On looking at any section of these buildings it wilj be seen how impossible it would have been for the passages to have belonged to a smaller structure (Petrie, 165). The supposition that the designs were enlarged so long as the builder's life permitted was drawn from the compound mastabas of Sakkara and Medum; these are, however, quite distinct architecturally from true pyramids, and appear to have been enlarged at long intervals, being elaborately finished with fine casing at the close of each addition.

The usual construction is a mass of masonry composed of horizontal layers of rough-hewn blocks, with a small amount of mortar; and this mass in the later forms became more and more rubbly, until in the VIth Dynasty it was merely a cellular system of retaining walls of rough atones and mud, filled up with loose chips, and in the Xllth Dynasty the bulk was of mud bricks. Whatever was the hidden material, however, there was always on the outside a casing of fine stone, elaborately finished, and very well jointed; and the inner chambers were of similarly good work. Indeed the construction was in all cases so far sound that, had it not been for the spite of enemies and the greed of later builders, it is probable that every pyramid would have been standing in good order at this day. The casings were not a mere "veneer" or "film," as they have been called, but were of massive blocks, usually greater in thickness than in height, and in some cases (as at South Dahshur) reminding the observer of horizontal leaves with sloping edges.

Inside of each pyramid, always low down, and usually below the ground level, was built a sepulchral chamber; this was reached in all cases by a passage from the north, sometimes beginning in the pyramid face, sometimes descending into the rock on which the pyramid was built in front of the north side. This chamber, if not cut in the rock altogether (as in Menkaura's), or a pit in the rock roofed with stone (as in Khafra's), was built between two immense walls which served for the east and west sides, and between which the north and south sides and roofing stood merely in contact, but unbonded. The gable roofing of the chambers was formed by great sloping cantilevers of stone, projecting from the north and south walls, on whxh they rested without pressing on each other along the central ridge; thus there was no thrust, nor were there any forces to disturb the building; and it was only after the most brutal treatment, by which these great masses of stone were cracked asunder, that the principle of thrust came into play, though it had been provided for in the sloping form of the roof, so as to delay as long as possible the collapse of the chamber.

This is best seen in the pyramid of Pepi, opened from the top right through the roof. See also the Abusir pyramids and the king's and queen's chambers of the great pyramid. The roofing is sometimes, perhaps usually, of more than one layer; in Pepi's pyramid it is of three layers of stone beams, each deeper than their breadth, resting one on another, the thirty stones weighing more than 30 tons each. In the king's chamber successive horizontal roofs were interposed between the chamber and the final gable roof, and such may have been the case at Abu Roash.

The passages which led into the central chambers have usually some lesser chamber in their course, and are blocked once or oftener with massive stone portcullises. In all cases some part, and generally the greater part, of the passages slopes downwards, usually at an angle of about 26°, or 1 on 2. These passages appear to have been closed externally with stone doors turning on a horizontal pivot, as may be seen at South Dahshur, and as is described by Strabo and others. This suggests that the interiors of the pyramids were accessible to the priests, probably for making offerings; the fact of many of them having been forcibly entered otherwise does not show that no practicable entrance existed, but merely that it was unknown, as, for instance, in the pyramids of Khufu and Khafra, both of which were regularly entered in classical times, but were forced by the Arabs.

How did the Egyptians know exactly where to put the enormously heavy building blocks? And how was the master architect able to communicate detailed, highly precise plans to a workforce of 10,000 illiterate men? Ole J. Bryn, an architect and associate professor at Norwegian University of Science and Technology (NTNU) concluded that the Egyptians invented the modern building grid, by separating the structure’s measuring system from the physical building itself, thus introducing tolerance, as it is called in today’s engineering and architectural professions.

No indication of the mechanical contrivances used for this purpose has been left, though that they possessed such can hardly be doubted. The fact that an almost fabulous number of laborers were engaged in erecting these pyramids did not lessen the necessity for the employment of certain machines. Egyptologists are consistently confronted by unanswered questions: How is it possible that some of the blocks are so perfectly matched that not even a human hair can be inserted between them? Why, despite the existence of millions of tons of stone, carved presumably with copper chisels, has not one copper chisel ever been found on the Giza Plateau?

The widely accepted theory -- that the pyramids were crafted of carved-out giant limestone blocks that workers carried up ramps -- was not embraced by everyone. Joseph Davidovits, director of the Geopolymer Institute in St. Quentin, France and a chemist at Barry University, Florida, claimed in 1984 that the stones of the pyramids were actually made of a very early form of concrete created using a mixture of limestone, clay, lime and water. From chemical analysis of the pyramid blocks, Davidovits found that limestones from the Turah and Mokattam quarries near Cairo are made of tight calcite crystals, whereas construction stones of the pyramids are considerably less dense and contain many bubbles. He also noted that the limestones of the pyramids contain up to 13% impurities, within the calcium carbonate, such as sodium carbonate, phosphate and silt, which he suggested must have come from the Nile.

In 2007 National Science Foundation-supported researcher Michel Barsoum, of the Department of Materials Science and Engineering at Drexel University, found that the tiniest structures within the inner and outer casing stones were indeed consistent with a reconstituted limestone. The cement binding the limestone aggregate was either silicon dioxide (the building block of quartz) or a calcium and magnesium-rich silicate mineral.

The stones also had a high water content - unusual for the normally dry, natural limestone found on the Giza plateau--and the cementing phases, in both the inner and outer casing stones, were amorphous, in other words, their atoms were not arranged in a regular and periodic array. Sedimentary rocks such as limestone are seldom, if ever, amorphous. The sample chemistries the researchers found do not exist anywhere in nature. Therefore, it's very improbable that the outer and inner casing stones that were examined were chiseled from a natural limestone block.

But the similarity of the blocks that now comprise the major pyramids of the Giza area to the massive Eocene Mokattam limestones that underlie the pyramids have long since been considered as essentially proven. To those familiar with limestone textures, there is no question about their natural occurrence and origin. The only question is the source quarries.

The mortar used in construction of the Egyptian pyramids was used to fill cracks and voids; it significantly enhanced the structural properties of the pyramids. A calcium sulfate-based mortar was used as a cementitious material and as a filler for cracks and open spaces in the Egyptian pyramids. The main constituents of this calcium sulfate-based material are gypsum, anhydrite, calcite, argillaceous limestone, and quartz sand. When the quarried gypsum bedrock was heat treated, it possessed pozzolanic properties due to the breakdown of clay to amorphous aluminosilicates. The term pozzolanic refers to a chemical reactionthat allows silica combined with lime to form a solid cementing material. This chemical reaction is driven by the addition of the pozzolanic material. While the original pozzolanic material was volcanic ash, modern pozzolans include materials such as fly ash and silica fume, which areindustrial byproducts.