Over the years many theories have been put forward to explain how ancient Egyptians moved the massive amounts of stone required to construct the pyramids. These theories have ranged from alien intervention to elaborate pulley and ramp systems.

Recently a team of physicists from the University of Amsterdam came up with a simple solution and UFO enthusiasts will be disappointed. The researchers noticed that a wall painting in the tomb of the Middle Kingdom pharaoh Djehutihotep shows a person pouring water over the sand in front of a sledge. Knowing that firm sand offers less resistance than loose sand and that firm sand wouldn’t pile up in front of the sledge, the researchers ran some tests.

The team placed a laboratory version of an Egyptian style sledge in a tray of sand. They tested the sledge using different consistencies of sand. They used a rheometer, a device which tests the way liquid flows in response to applied force, to determine how much force was needed to move the wet sand.

The experiment showed that the stiffer the sand was the less force was required to move an object across it. Sand that was too wet would also slow down the sledge. However, with the optimal amount of moisture the force required to pull the sledge was reduced by half.

“Capillary bridges arise when water is added to the sand. These are small water droplets that bind the sand grains together. In the presence of the correct quantity of water, wet desert sand is about twice as stiff as dry sand. A sledge glides far more easily over firm desert sand simply because the sand does not pile up in front of the sledge as it does in the case of dry sand,” according to a statement from the university.

The research, led by professor Daniel Bonn, was part of the Fundamental Aspects of Friction program. The full paper can be found in the journal Physical Review Letters.