Stones which make up the pyramids weigh up to 2.5 tons each, and were transported without wheels, from many miles away. Based on a new study, ancient Egyptians may have done this by placing the massive blocks on sleds. As these were pulled along the ground, workers may have wet the area directly in front of the travel path. By doing this, the number of workers needed to pull the stones may have been reduced by half.
As water is poured on sand, the moisture creates "bridges" between the individual grains, locking them in place. This creates a surface twice as firm as sand alone, preventing the material from piling up in front of the sled. The procedure is similar to using wet sand to create a sand castle on a beach. While wet, sand can be shaped and formed, but dry material offers little structure or formation.
"The formation of capillary water bridges increases the shear modulus of the sand, which facilitates the sliding. Too much water, on the other hand, makes the capillary bridges coalesce, resulting in a decrease of the modulus; in this case, we observe that the friction coefficient increases again," researchers wrote in the article announcing the study.
Much like sand castles, too much water causes the once-firm material to turn to mud, which would have made it difficult to transport the building blocks.
"The physicists placed a laboratory version of the Egyptian sledge in a tray of sand. They determined both the required pulling force and the stiffness of the sand as a function of the quantity of water in the sand. To determine the stiffness they used a rheometer, which shows how much force is needed to deform a certain volume of sand," investigators wrote in a press release announcing their findings.
A picture painted on an ancient Egyptian tomb shows the process in action. As slaves pull a sled loaded with a massive statue, another worker is pouring water on the sand, in front of the hand-drawn vehicle. This painting was discovered during the Victorian Era, in the tomb of Djehutihotep, a pharaoh who lived around the year B.C.E. 1900.
Study of how water may have assisted building of the pyramids was published in the journal Physical Review Letters.