Construction of the Egyptian pyramids
The construction of the Egyptian pyramids can be explained with well-established scientific facts; however, there are some aspects that even today are considered controversial hypotheses. The construction techniques used seem to have developed over time; later pyramids were not constructed in the same way as earlier ones. It is believed that huge stones were carved from quarries with copper tools, and these blocks were then dragged and lifted into position. Disagreements chiefly concern the methods used to move and place the stones.
In addition to the many unresolved arguments about the construction techniques, there have been disagreements as to the kind of workforce used. The Greeks, many years after the event, believed that the pyramids were built by slave labour. Archaeologists now believe that the Great Pyramid of Giza was built by tens of thousands of skilled workers who camped near the pyramids and worked for a salary or as a form of tax payment until the construction was completed, pointing to workers' cemeteries discovered in 1990. For the Middle Kingdom pyramid of Amenemhat II, there is evidence from the annal stone of the king that foreigners from Canaan were employed.
The pseudoscientific field of pyramidology includes many archaeological fringe theories attempting to explain how the pyramids were built.
Historical hypotheses
The Writing of Herodotus and Diodorus Siculus
The first historical accounts of the construction of these monuments came centuries after the era of pyramid construction, by Herodotus in the 5th century BC and Diodorus Siculus in the 1st century BC. Herodotus's account claims that the Egyptians used a machine, stating:Diodorus Siculus's account states:
Diodorus Siculus's description of the shipment of the stone from Arabia is correct since the term "Arabia" in those days implied the land between the Nile and the Red Sea where the limestone blocks have been transported from quarries across the river Nile.
Materials
Third through Fifth dynasties
During the earliest period, pyramids were constructed wholly of stone. Locally quarried limestone was the material of choice for the main body of these pyramids, while a higher quality of limestone quarried at Tura was used for the outer casing. The limestone originated from different outcrops of the Eocene-aged Mokattam Formation. Granite, quarried near Aswan, was used to construct some architectural elements, including the portcullis and the roofs and walls of the burial chamber. Occasionally, granite was used in the outer casing as well, such as in the Pyramid of Menkaure. In the early pyramids, the layers of stone forming the pyramid body were laid sloping inwards; however, this configuration was abandoned in later pyramids. The Bent Pyramid at Dahshur seems to indicate acceptance of a new technique at a transition between these two building techniques. Its lower section is built of sloping courses while in its upper section the stones are laid horizontally.Middle Kingdom and onward
During the Middle Kingdom, pyramid construction techniques changed again. Most pyramids built then were little more than mountains of mud-brick encased in a veneer of polished limestone. In several cases, later pyramids were built on top of natural hills to further reduce the volume of material needed in their construction. The materials and methods of construction used in the earliest pyramids have ensured their survival in a generally much better state of preservation than for the pyramid monuments of the later pharaohs.Mortar
The stones forming the core of the pyramids were roughly cut, especially in the Great Pyramid. To fill the gaps, huge quantities of gypsum and rubble were needed. The filling has almost no binding properties, but it was necessary to stabilize the construction. To make the gypsum mortar, it had to be dehydrated by heating which requires large quantities of wood. According to Egyptologists, the findings of both the 1984 and 1995 David H. Koch Pyramids Radiocarbon Projects may suggest that Egypt had to strip its forest and scrap every bit of wood it had to build the pyramids of Giza and other even earlier 4th Dynasty pyramids. Carbon dating samples from core blocks and other materials revealed that dates from the 1984 study averaged 374 years earlier than currently accepted and the 1995 dating averaging 100–200 years. As suggested by team members, "We thought that it was unlikely that the pyramid builders consistently used centuries-old wood as fuel in preparing mortar. The 1984 results left us with too little data to conclude that the historical chronology of the Old Kingdom was wrong by nearly 400 years, but we considered this at least a possibility". Egyptologists propose that the old wood problem is responsible for the discrepancy, claiming the earlier dates were possibly derived from recycling large amounts of centuries-old wood and other earlier materials.Arsenical copper
The main material used in the Old and Middle Kingdoms was so-called arsenical copper or bronze. It is more effective than copper with minor impurities, and can be made even harder by repeated hammering. Hundreds of artefacts from these periods were made of this material. All preserved copper alloy tools of the Old Kingdom era of pyramid builders were recently collected in a monograph. Its occurrence was also confirmed for the settlement material from Giza, from the reigns of Khufu and Khafre. Recent data from Middle Kingdom Elephantine Island indicate that this material was an intentionally produced alloy, and a result of rather complex technology.Quarrying
There is good information concerning the location of the quarries, some of the tools used to cut stone in the quarries, transportation of the stone to the monument, leveling the foundation, and leveling the subsequent tiers of the developing superstructure. Workmen probably used copper chisels, drills, and saws to cut softer stone, such as most of the limestone. The harder stones, such as granite, granodiorite, syenite, and basalt, cannot be cut with copper tools alone; instead, they were worked with time-consuming methods like pounding with dolerite, drilling, and sawing with the aid of an abrasive, such as quartz or corundum sand. This occurred in a process known as sand abrasion. Blocks were transported by sledge likely lubricated by water.Leveling the foundation may have been accomplished by use of water-filled trenches as suggested by Mark Lehner and I. E. S. Edwards or through the use of a crude square level and experienced surveyors.
Transport of stone blocks
One of the major problems faced by the early pyramid builders was the need to move huge quantities of stone. The Twelfth Dynasty tomb of Djehutihotep has an illustration of 172 men pulling an alabaster statue of him on a sledge. The statue is estimated to weigh 60 tons and Denys Stocks estimated that 45 workers would be required to start moving a lubricated block, or eight workers to move a block. Dick Parry and Mladjov have suggested a method for rolling the stones, using a cradle-like machine that had been excavated in various new kingdom temples. Four of those objects could be fitted around a block so it could be rolled easily. Experiments done by the Obayashi Corporation, with concrete blocks square by long and weighing, showed how 18 men could drag the block over a 1-in-4 incline ramp, at a rate of. This idea was previously described by John Bush in 1977, and is mentioned in the Closing Remarks section of Parry's book. Vitruvius in De architectura described a similar method for moving irregular weights. It is still not known whether the Egyptians used this method but the experiments indicate it could have worked using stones of this size. Egyptologists generally accept this for the 2.5 ton blocks mostly used but do not agree over the methods used for the 15+ ton and several 70 to 80 ton blocks.The diary of Merer, logbooks written more than 4,500 years ago by an Egyptian official and found in 2013 by a French archeology team under the direction of Pierre Tallet in a cave in Wadi al-Jarf, describes the transportation of limestone blocks from the quarries at Tura to Giza by boat.
Ramps
Most Egyptologists acknowledge that ramps are the most tenable of the methods to raise the blocks, yet they acknowledge that it is an incomplete method that must be supplemented by another device. Archaeological evidence for the use of ramps has been found at the Great Pyramid of Giza and other pyramids. The method most accepted for assisting ramps is levering. The archaeological record gives evidence of only small ramps and inclined causeways, not something that could have been used to construct even a majority of the monument. To add to the uncertainty, there is considerable evidence demonstrating that non-standardized or ad hoc construction methods were used in pyramid construction.Therefore, there are many proposed ramps and there is a considerable amount of discrepancy regarding what type of ramp was used to build the pyramids. One of the widely discredited ramping methods is the large straight ramp, and it is routinely discredited on functional grounds for its massive size, lack of archaeological evidence, huge labor cost, and other problems.
Other ramps serve to correct these problems of ramp size, yet run into critiques of either functionality or limited archaeological evidence. Zig-zagging ramps, straight ramps using the incomplete part of the superstructure, spiraling ramps supported by the superstructure and spiraling ramps leaning on the monument as a large accretion have been proposed. Mark Lehner speculated that a spiraling ramp, beginning in the stone quarry to the southeast and continuing around the exterior of the pyramid, may have been used. However, spiral ramps would have covered the building for decades fully and would not allow the regular layout of the exact pyramid square in equal distance to each base cornerstone as the only method to keep the exact geometric shape of the edges and side mantles. Ramp models with several ramp paths, which are positioned on the inner step pyramid require relatively less material. The stone blocks may have been drawn on sleds along the ramps lubricated by water.
As a recent study shows that the challenge was not just to account for the route the transported stones had to take but to account for the size and frequency of stones being moved—circa 1 ton being put in place every 2–3 minutes by human draw teams on a ramp of maximum 10%—to enable building of the Great Pyramid within 30 years. The special case of the pyramid extensions E2 and E3 in Meydum of ring-shaped extensions only wide around the previous building core shows the ramp system was effective and small in volume which applies for tangential ramps of 10 cubits or 5 metre width. The challenge was the geometry of the pyramid that provides shorter side lengths the higher the building grows, increases the necessity to turn maneuvers and allows less space for ramps leaning on the masonry. The slope change of the Bent Pyramid is probably the result of the discovery this can not be solved with steep gradients. Also essential was the effective organization of the building site by a module that allowed the work division of the teams along plots and the transport causeways between ramp and workplace, including the return of pulling crews and sleds, probably by a second ramp system. The problem of building the mantle at the ramp arrival point could be solved by bypass-systems.