One of the Seven Wonders of the World
The Great Pyramid of Khufu was one of the Seven Wonders of the World to the ancients and we still marvel at it today. Although it is not the largest pyramid of the past –– honors go to an otherwise undistinguished pyramid from Cholula, Mexico, that was built about half as far back –– Khufu’s pyramid amazes because of its antiquity, the size of its stones, the perfection of its orientation, and its many hidden chambers. Outwardly about as simple as an edifice can be, the Great Pyramid is actually a complex and interesting object. Furthermore, it is flanked by two nearby pyramids, each almost as large, that would be wonders by themselves if the Great Pyramid had never been built.
Writings about two millennia after construction of the pyramids
The Greek historian Herodotus, writing about two millennia after construction of the pyramids, claimed that it took teams of 100,000 men at a time working for 20 years to build them. Herodotus also claimed that the ancient Egyptians had marvelous machines that they used to lift the stones into place. Neither of these claims seems to be true.
A current misconception is that the Egyptians moved the large stones on rollers made from tree trunks. According to this theory, by having teams constantly replenish the front rollers with those
from the rear, it should have been possible to move a stone almost as if the wheel had been invented. This is idle speculation with no evidence in its favor and much circumstantial evidence against it.
The most reliable clues to Egyptian construction methods
The most reliable clues to Egyptian construction methods are the wall paintings from ancient Egypt, although many of the most suggestive are far from contemporaneous with the pyramids. Using
such paintings and some related texts, along with practices employed in more recent times and a few artifacts, we can put together the following scenario:
Decent limestone beds on the same side of the river as the pyramids and good limestone from the far side were used. Limestone was cut in blocks by making notches with hard rock, inserting wooden wedges, and wetting the wedges. When the wedges swelled, the stone fractured. Sometimes copper wedges in increasing sizes were used instead. Granite, used for plugs and caps, may have been cut by pounding it with a harder stone.
Very heavy objects, some ten times the weight of pyramid stones, are shown in wall paintings as being moved on sledges, not on rollers or wheels, considerably later than when the pyramids were built. Wheels were new in Mesopotamia around the time of the pyramids, but word had not reached Egypt. The sledges were aided by pouring a liquid in their path to lubricate the way. Some have speculated that the liquid was milk, but vegetable oil of some kind seems within the abilities of Egyptians of the time (and much more efficient).
Anyone who has tried to make a large region level knows that it is far from easy, but the base of the Great Pyramid is much more level than the foundations of many modern buildings. Farmers today use lasers to level fields, but ancient Egyptians probably used shallow ponds. A brick or mud wall can be used to enclose the site. Introduce water to make a pond; its surface will be level. Then drill holes to a fixed depth below the surface. Remove the water; the bases of the holes mark the level
surface; just remove everything down to this base.
Although most people think of lifting or transporting the stones as the most difficult part of building a pyramid in ancient times, orienting it so that one side of the base is perfectly north-south is much more difficult. For one thing, there was no pole star 5000 years ago; Earth’s axis moves in a circle once each 26,000 years. At sea, it is possible to use the rising and setting of any bright star to find north; the bisector of the angle between such a rising and setting will be either due north or due south. But that method relies on the nearly level circular horizon provided by the sea, which is not available where the pyramids were built. But since the Egyptians knew how to make a level surface,
they could build a semicircular wall with a level top and use that as an artificial horizon.
Perhaps even more difficult than finding north or south is finding true east and west. Egyptian masons commonly worked with the tool that we call a square, and square corners are common in Egyptian buildings. But the squareness of the Great Pyramid is so good that something more accurate must have been employed. It is known that more than a thousand years later Egyptian surveyors used a rope knotted to make a right 3-4-5 triangle. If the sides are measured accurately, such a triangle will give a perfect right angle. Also later Egyptians probably knew that an angle inscribed in a semicircle is always a right angle.
Keeping the slope of the sides the same over an area of 31,000 sq m (7.7 acres) was another difficult task. It seems likely that the masons used the diagonals of the square to locate its center and erected a vertical pole (using their ability to find right angles) to the planned height of the finished pyramid. They could then sight to find the correct slope. An error in this procedure might have accounted for the Bent Pyramid of Seneferu (c.2650 BCE) at Dajshur, although the change in slope halfway up from about 54° to about 43° is usually ascribed to running low on money before the pyramid was complete.
This is the easy part. Instead of lifting the stones, some as heavy as 150 tons (although the average limestone block was only about 2.5 tons), the Egyptians built long ramps to the working level so that stones could be moved up on sledges. Then levers and wedges were used to put the stones in place.
The outer blocks were cut in final form and lowered very carefully so that the process would not damage the facing. It is thought that this was accomplished by lowering from one set of wooden braces to another, with each set of braces only about a centimeter (half an inch) lower than the one above it.