The mystery of how the Egyptians built the pyramids without modern technology has long puzzled scientists and Egyptologists alike.
But now researchers from the University of Amsterdam think they've found the secret - and it all comes down to friction.
Back in the day, the ancient Egyptians transported these massive stones on large flat sleds with upturned edges across the desert from the quarries where they were made.
But in experiments replicating these conditions, scientists found the sled kept sinking into the sand, causing a sand bank to build up in front and making it almost impossible to move.
Unless, it turns out, the sand was wet.
The scientists have discovered that by creating just the right amount of moisture in the sand, Egyptians were able to create a much firmer surface and reduce the force required to drag the sled in half.
To test their theory, the physicists placed a lab version of the Egyptian sledge in a tray of sand and determined the required pulling force and stiffness of the sand depending on how much moisture was present.
Their results, published in Physical Review Letters, revealed that the required pulling force decreased as the sand got wetter and firmer. This occurs because of capillary bridges - where microdroplets of water bind grains of sand to one another through capillary action - as Gizmodo explains.
And in hindsight, we probably should have figured this out earlier, the researchers believe.
The University of Amsterdam press release explains: "These experiments served to confirm what the Egyptians clearly already knew, and what we probably already should have. Artwork within the tomb of Djehutihotep, which was discovered in the Victorian Era, depicts a scene of slaves hauling a colossal statue of the Middle Kingdom ruler and in it, a guy at the front of the sled is shown pouring liquid into the sand. You can see it in the image above, just to the right of the statue's foot."
Well, this is embarrassing. Maybe someone should also try physics to solve the mystery of how Stonehenge got there.