Scientists and conspiracy theorists have long wondered how Egyptians transported pyramid stones. Now, thanks to physicists from the University of Amsterdam, the mystery has been solved.

Physicists have found that the ancient Egyptians utilized an ingenious technique to make moving heavy pyramid stones by sledge more tolerable, giving them the ability to halve the number of workers required.

To construct the pyramids, workers had to move massive blocks of stone and big statues across the desert. The weighty objects were positioned on a sledge and pulled over the sand. Physicists have demonstrated that the Egyptians likely made the sand in front of the sledge wet. In fact, the right amount of dampness in the sand cuts the pulling force needed in half.

The physicists constructed a laboratory version of the sledge and placed it in a tray of sand. They calculated both the necessary pulling force and the stiffness of the sand as a function of the amount of water in the sand.

The physicists discovered that the necessary pulling force lessened proportional to the stiffness of the sand. Capillary bridges emerge when water is added to the sand. These are tiny water droplets that bind the sand grains together. With the right amount of water, wet desert sand is approximately twice as stiff as dry sand. A sledge can be pulled more easily over stiff desert sand because the sand does not accumulate in front of the sledge.

A wall painting in the tomb of Djehutihotep, which clearly depicts a person standing on the front of a sledge and pouring water over the sand, suggests that the Egyptians knew about this clever trick.

The study’s findings are described in greater detail in the journal Physical Review Letters.