A Damp Solution to the Mystery of the Pyramids?
May 5, 2104
The ancient Egyptians may have used a remarkably simple technique to move massive limestone blocks across the sand to build the pyramids, according to a team of scientists led by Daniel Bonn at the University of Amsterdam in the Netherlands. The scientists claim that the technique would have greatly reduced both the amount of time and human labor needed build the structures. The solution is familiar to anyone who has ever built a sand castle at the beach–wet sand.
From about 2700 to 1700 B.C., the ancient Egyptians built 35 massive pyramids near the Nile River to protect the bodies of the pharaohs in the afterlife. Some of these pyramids. those located at Giza, are among the Seven Wonders of the Ancient World. The largest Egyptian Pyramid, the Great Pyramid of Khufu, was constructed from more than 2 million stone blocks that average 2.5 tons (2.3 metric tons) each.
Over the years, scholars have proposed many theories to explain how the ancient Egyptians achieved this feat with only simple copper tools and manual labor. Some theories involved elaborate systems of greased ramps, sleds, pulleys, and the brute force of tens of thousands of workers. Others have suggested the ancient Egyptians possessed advanced technical knowledge or sources of energy that are now lost to history.
The pyramids of Egypt at Giza are the best preserved of the Seven Wonders of the Ancient World. They still attract many visitors to Giza, just outside the present-day city of Cairo. (World Book illustration by Birney Lettick)
In a series of simple experiments, Bonn and his team demonstrated that adding a small amount of water to sand greatly reduces friction, making it much easier to slide an object–even a very heavy object–over it. When they pulled a heavy sled through dry sand, they found the front of the sled tended to dig in as loose sand piled up in front, stalling further movement. However, when water was added to dry sand, the force needed to pull the sled decreased. In sand with just the right amount of dampness, water binds grains of sand together through capillary action. This increases the stiffness of the sand and prevents the sled from digging in and stalling. The scientists found that wet sand could cut the force required to drag a sled weighing several tons by about half.
Although there is virtually no physical evidence or written records that describe the construction of the pyramids, Bonn is confident that the ancient Egyptians would have known of the friction-reducing properties of wet sand. Artwork discovered more than 100 years ago in an Egyptian tomb provides a clue that he is right. The tomb includes a painting of workers hauling a colossal statue on a wooden sled. One figure at the front of the sled is shown pouring water from a clay jar into the sand below.
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