Egyptologists believe the pyramid was built as a tomb for the Fourth Dynasty Egyptian pharaoh Khufu (often Hellenized as "Cheops") and was constructed over a 20-year period. Khufu's vizier, Hemiunu (also called Hemon) is believed by some to be the architect of the Great Pyramid. It is thought that, at construction, the Great Pyramid was originally 280 Egyptian Royal cubits tall (146.5 metres (480.6 ft)), but with erosion and absence of its pyramidion, its present height is 138.8 metres (455.4 ft). Each base side was 440 cubits, 230.4 metres (755.9 ft) long. The mass of the pyramid is estimated at 5.9 million tonnes. The volume, including an internal hillock, is roughly 2,500,000 cubic metres (88,000,000 cu ft).
Based on these estimates, building the pyramid in 20 years would involve installing approximately 800 tonnes of stone every day. Additionally, since it consists of an estimated 2.3 million blocks, completing the building in 20 years would involve moving an average of more than 12 of the blocks into place each hour, day and night. The first precision measurements of the pyramid were made by Egyptologist Sir Flinders Petrie in 1880–82 and published as The Pyramids and Temples of Gizeh. Almost all reports are based on his measurements. Many of the casing-stones and inner chamber blocks of the Great Pyramid fit together with extremely high precision. Based on measurements taken on the north-eastern casing stones, the mean opening of the joints is only 0.5 millimetre wide (1/50 of an inch).
Great Pyramid of Giza from a 19th-century stereopticon card photo
The pyramid remained the tallest man-made structure in the world for over 3,800 years, unsurpassed until the 160-metre-tall (520 ft) spire of Lincoln Cathedral was completed c. 1300. The accuracy of the pyramid's workmanship is such that the four sides of the base have an average error of only 58 millimetres in length. The base is horizontal and flat to within ±15 mm (0.6 in). The sides of the square base are closely aligned to the four cardinal compass points (within four minutes of arc)[9] based on true north, not magnetic north, and the finished base was squared to a mean corner error of only 12 seconds of arc.
The completed design dimensions, as suggested by Petrie's survey and subsequent studies, are estimated to have originally been 280 Egyptian Royal cubits high by 440 cubits long at each of the four sides of its base. The ratio of the perimeter to height of 1760/280 Egyptian Royal cubits equates to 2π to an accuracy of better than 0.05 percent (corresponding to the well-known approximation of π as 22/7). Some Egyptologists consider this to have been the result of deliberate design proportion. Verner wrote, "We can conclude that although the ancient Egyptians could not precisely define the value of π, in practice they used it".Petrie, author of Pyramids and Temples of Gizeh concluded: "but these relations of areas and of circular ratio are so systematic that we should grant that they were in the builder's design".Others have argued that the Ancient Egyptians had no concept of pi and would not have thought to encode it in their monuments. They believe that the observed pyramid slope may be based on a simple seked slope choice alone, with no regard to the overall size and proportions of the finished building. In 2013, rolls of papyrus called the Diary of Merer were discovered written by some of those who delivered limestone and other construction materials from Tora to Giza.
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