Under the Microscope/Prof William Reville: A colleague once remarked that of all the natural wonder of the world he had seen, the only one to exceed his expectations were the pyramids of Egypt - the largest monuments ever built.
Constructed more than 4,000 years ago, they still inflame the human imagination, and theories abound as to their construction and function. The pyramids are the ultimate demonstration of the influence of architecture.
The pyramids were built over a period of 2,500 years, but mainly between 2,686 BC and 2,181 BC. More than 80 pyramids exist, but the three greatest are the pyramids at Gizeh, including the great pyramid of Cheops, the largest pyramid of all. It is estimated that this pyramid contains 2,300,000 blocks, each weighing on average 2.5 tonnes - a total of 6.5 million tonnes. Some blocks weigh up to 20 tonnes. The volume of the great pyramid could easily accommodate the cathedrals of Milan, Florence, St Peter's in Rome, Westminster Abbey and St Paul's cathedral in London. Napoleon estimated that the three pyramids at Gizeh had enough stone to build a wall 10 feet high and one foot wide around France.
The square base of the great pyramid has sides of 230.4 metres (756 feet) and an area of over 13 acres. The original height of the pyramid was almost 147 metres (481 feet). The faces of all pyramids in Egypt, except two, are inclined at an angle of 52 degrees to the horizontal. The two exceptions show an angle of 43.5 degrees. Some scholars have inferred that the Egyptians accurately knew the value of the ratio of the circumference to the diameter of a circle, the famous number pi. However, this is unlikely, and several mechanisms have been proposed by which the Egyptians could have measured these angles without knowing pi.
The pyramids contain three kinds of blocks - core blocks of local limestone surrounded by casing blocks cut with great accuracy out of the same stone, and facing blocks of limestone carried to the site by boat from quarries up the Nile. Skilled masons smoothed these facing blocks and fitted them together so well that a postcard cannot be inserted between them. Stones in the quarries were probably cut by pounding them with a lump of dororite (a hard igneous rock), wedging wood into the resulting cuts in the softer limestone, thereby cracking the limestone along horizontal and vertical planes.
How did a civilisation with no metal stronger than copper and without wheels construct these massive monuments? Blocks were moved to the sites on sledges, pulled over land by men with enormous effort. The average pyramid block weighs 2.5 tonnes but granite slabs in the King's chamber of the great pyramid weigh 50 tons. It seems likely that lifting gear involving levers and counter weights were used to manoeuvre blocks into their final precise positions.
Kurt Mendelssohn, a German pyramidalogist, has estimated the labour that built the main pyramids at Meidum, Dashur, and Gizeh over a period of 100 years. These pyramids called for 25 million tons of materials. The workers were divided into two groups. Unskilled masons quarried local stone, built ramps, lifted blocks, and lubricated sledges. Skilled masons cut, prepared and set the casing and finishing stones. The first group was employed seasonally during Nile floodings and may have been 70,000 strong. The second group was permanently employed and may have numbered around 10,000.
The principal function of the pyramids was to serve as tombs for the Pharaohs, although some were simply monuments. After death the Pharaoh was identified with the sun-god. The body was mummified, wrapped in resin-soaked linen, enclosed in a coffin and set in a sarcophagus of stone within the pyramid. The pyramid shape was possibly suggested by pyramids of light sometimes seen to project onto the land when sunrays over the Nile pierce the clouds of a heavy sky.
Pyramid-building had huge social consequences. When King Menes of southern upper Egypt conquered northern lower Egypt the administration of the united kingdom was centralised. The king was deified, helping to unite the populations of the two separate kingdoms after a long conflict. The pyramid age began and a draft was established to effect the massive constructions. This helped to assure economic equality for the peasants of the 42 provinces who were probably eager to work during the flood periods in return for food.
Some Pharaohs reigned for decades, some for only a few years, and some built more than one pyramid during their reign. A pyramid begun during the reign of a short-lived Pharaoh would be completed during the reign of his successor, and a new pyramid begun for the successor.
Pyramid building became a continuous process which welded the provinces into a modern state. The continuous nature of the process was essential because to send 150,000 men home when a pyramid was completed would disrupt the economic and labour balance of the kingdom. The essential modern features of a centralised administration were developed at this time. Pyramid building probably became the most important justification of the state. Further details can be read in Why Buildings Stand Up by M Salvadori (WW Norton, 2002).
William Reville is associate professor of
biochemistry and director of microscopy at University College Cork