August 2011

Historical Metallurgy

Industrial minerals in history: Ancient Egypt

By Fathi Habashi, Laval University, Quebec City

 

The pyramids near Giza; the Great Pyramid (the one at the back) was finished by Khufu around 2551 BC


Large-scale quarrying began in Ancient Egypt. The procurement of stone was essential to the social and economic aspects of life. Quarrying produced raw materials from which important items of religious and funerary architecture and equipment were made. The number of workers sent out by the pharaoh on quarrying expeditions to remote mining areas in the deserts was comparable to that of a military campaign – upwards of tens of thousands – and included stone cutters, professionals, an administrative staff, stone masons, soldiers, guards and enslaved prisoners for transporting blocks. Housing settlements were provided for the workers. The miners felt protected on their expeditions by the Egyptian goddess Hathor.

The construction of the pyramids, transportation of massive rocks, and extensive working of hard rock such as granite was conducted on an unprecedented scale. The ancient Egyptians quarried tremendous quantities of limestone; large quantities of granite from Aswan; alabaster, diorite, marble, serpentine, purple porphyry and black slate from Wadi Rahanu; basalt, dolomite and other ornamental stones. They also mined for precious stones such as turquoise, emeralds, malachite, amethyst as well as other gemstones.

Salt was obtained by evaporating seawater in shallow lagoons on the Mediterranean coast and from deposits in the Western and Eastern deserts. Natron, a naturally occurring sodium carbonate, was found in a deposit 20 metres below sea level in the Wadi al-Natrun, halfway between Cairo and Alexandria. It was used mainly for cleaning and in the mummification process. Alum, used for dying cloth, was found in the oases of Dakla and Kharga in the Western Desert.

Quarrying and stone cutting in Ancient Egypt was an unprecedented activity. The tools used for quarrying soft stones were perhaps made of a hard stone such as basalt or dolerite, weighing between one and three kilograms. For hard stone, the excavation of open-cast quarries was conducted with hammer stones, which gradually removed the desired stone from the surface, working downward. Once the chosen area of rock had been roughly evened out, it was probably strewn with glowing pieces of charcoal and then doused with cold water. The surface of the stone would disintegrate at this point, making the block easier to extract.

During the New Kingdom and in later periods, workmen used pointed chisels that were hammered with a mallet. It is also possible that soft stone was sometimes cut with copper saws that had a toothed edge embedded with grains of sand during the forging process. Iron was not yet known and, thus, copper chisels must have been used. There were extensive quarry operations in and around Aswan that continued unabated during the Roman period.

The pyramids

The first use of limestone on a large scale as a construction material was for the Step Pyramid at Saqqara. There are about 100 pyramids in Egypt, the largest ones located in Memphis (present day Giza). The Great Pyramid is made up of about 2.3 million large limestone blocks, each weighing about 2.5 tonnes; its total mass is estimated at 5.9 million tonnes. Building it in 20 years would have meant installing approximately 800 tonnes of stone, or 320 blocks, every day. The surfaces of the blocks were smooth so that they fit one on top of the other without mortar. An abrasive powder of crushed quartzite was used to smooth the faces (the grains were sharp-edged unlike the rounded ones of desert sand).

The Great Pyramid is not just a pile of stones; it is a grave with a burial chamber, passages and ventilation ducts – an engineering feat. The pharaoh was buried in a chamber in the centre of the pyramid, but at Saqqara, the pharaoh was buried underground. The burial chamber in the Great Pyramid was made entirely from massive blocks of granite.

Obelisks

An obelisk is a monumental tapered column carved from a single block of stone, with a square or rectangular cross-section and a gold-covered pointed top called a pyramidion.

Originating from the granite quarries of Aswan, obelisks generally were inscribed on all four sides. The average obelisk was about 30 metres high and weighed about 800 tonnes. They were set in pairs at the entrances of temples and some Old Kingdom tombs, and were closely related to the cult of the Sun God Ra (also known as Atum). There are 26 known ancient Egyptian obelisks located in many different countries, including the United Kingdom, the United States, France, Turkey and Italy. The obelisks in Rome were transported there during the time of Augustus.

In 1586, Italian engineer Domenico Fontana (1543-1607) moved the 331-tonne Egyptian obelisk to its present site in front of the Vatican in St. Peter’s Square. The obelisk, quarried in Egypt in the 13th century BC, was brought to Rome in the 1st century. It remained in place until Pope Sixtus V recommended moving the obelisk about 200 metres from its original Roman site. Fontana relied on pulleys, some as large as 1.5 metres in length, to lift the obelisk off its base and then lower it to a horizontal position by pivoting it on its lower end. Five huge levers, 16 metres long each, were used to help lift the shaft off the base. A variety of pulley blocks were required to work in conjunction with the 40 winches, each of which was powered with horses and men to supply the main lifting force. It took one year to complete the task. On September 28, 1586, the scaffolding and tower were removed. The obelisk appeared in full view, in the same position as it appears today, more than 400 years later.

An unextracted obelisk still remains within the layer of rock in Aswan. Estimated to weigh 1,200 tonnes, it would have been the tallest (41.7 metres) but was abandoned due to the appearance of fissures in the stone.

Memphis Serapeum

The Serapeum is a huge underground cemetery that was used by the ancient Egyptians to bury their 64 mummified sacred Apis bulls. Carefully selected by the priests, the bulls served as a physical manifestation of the god Ptah. The black bull-calf was thought to have been conceived by a ray from heaven and was treated like royalty during its lifetime (around 20 to 25 years) and in its funerary ceremonies.

The bulls were embalmed in the position of a sphinx and buried with great ceremony in the Saqqara catacombs near Memphis. Massive carved granite sarcophagi (each weighing about 70 tonnes) were used. The catacombs continued to be used until the Ptolemaic Period, when the Emperor Honorius banned it and closed the Serapeum in 398 AD.

Karnak

The temples of Ancient Egypt include some of the largest religious monuments the world has ever known and certainly some of the most impressive. In the temple of Amun at Karnak, the stone used in these structures came from nearby quarries and was usually sandstone or granite. The work was started by Seti I, but the majority of the construction was done by Ramses II. Because the building was done without mortar, the stones were cut with precision so they fit together perfectly.

The columns for the temples were cut into sections and they were placed on one top of the other until the desired height was reached. The Great Hall consists of 134 columns: 122 are 10 metres tall and the other 12 are 21 metres tall with a diameter of over three metres. The architraves on top of these columns weigh an estimated 70 tons.

Colossal sculptures

The ancient Egyptians not only quarried large masses of stone for constructing impressive structures, they also created artwork from them.

Transportation

The problem of transporting rock or building blocks over land with a soft subsoil was solved by loading the material onto sledges and hauling them over paths paved with transverse logs lubricated with fine mud. The sledges were made of solid baulks of wood, with two runners turned up in front. The method is illustrated in the scene from the 12th Dynasty tomb of the provincial prince Djehutihotep at el-Bersha, that shows his colossal statue on the move. The statue, which has been estimated to have weighed about 60 tonnes, was dragged on its sledge with ropes by 172 men in four files. The illustration shows a man standing at the foot of the figure pouring water onto the path in front of the sledge while others urge the team on. Three more men are bringing up fresh jugs of water and another three a large beam, perhaps used as a lever.

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