The pyramids of ancient Egypt have been a source of wonder for centuries. And though many of their secrets have been revealed and understood (and no, it wasn't that aliens built them), historians continue to struggle to explain how the Egyptians moved all the giant stones through the desert to be assembled into the spectacular pyramids they would eventually become.
A new study from researchers at the University of Amsterdam published in the Physical Review Letters argues it has finally answered that question, and the solution is surprisingly simple.
Wet sand. The Egyptians wet the sand in the desert to make it easier to pull the heavy stones on the primitive sledges they would have been using.
Daniel Bonn, a professor of physics at the University of Amsterdam and a lead author of the paper, said that he'd been inspired to study this puzzle after he came across a wall painting from the tomb of Djehutihotep which depicts an army of men pulling a massive statue on a sledge. At the front of the sledge, one man is shown pouring out water and for years, Egyptologists thought nothing of this, dismissing it as some sort of ritual. Bonn wasn't as convinced and started testing how wet sand might perform under these conditions. Soon after, he found success.
"For the construction of the pyramids, the ancient Egyptians had to transport heavy blocks of stone and large statues across the desert," the university said. "The Egyptians therefore placed the heavy objects on a sledge that workers pulled over the sand. Research ... revealed that the Egyptians probably made the desert sand in front of the sledge wet."
Image Credit: Wikicommons
Makes sense. And the physics to back it up is pretty straight-forward as well.
"When the sand was dry, a heap of sand formed in front of the sled, hindering its movement; a relatively high force was needed for the sled to reach a steady state. Adding water made the sand more rigid, and the heaps decreased in size until no heap formed in front of the moving sled and therefore a lower applied force was needed to reach a steady state," researchers note in their synopsis.
Simply put, with the right amount of water, the hot desert sand turned into a relatively smooth surface with reduced friction for easier pulling and just enough tension to support a large sledge without digging into the sand. Until now, it was entirely unclear how the Egyptians managed to move the massive blocks, but knowing how much they could have decreased the friction, the researchers are confident that the task would have been much more manageable with this one "handy trick."
"I was very surprised by the amount the pulling force could be reduced — by as much as 50% — meaning that the Egyptians needed only half the men to pull over wet sand as compared to dry," Bonn told the Washington Post.
Is that it? However, while this is certainly a clean and tidy explanation, Bonn's research only revealed that this technique works and would have been available to the Egyptians at the time. There's still no evidence that this was the exact or actual method used at the time. But given it's ease and function and considering how clever the ancient Egyptians were in so many other aspects of the pyramids' creation, it's a pretty likely solution and according to the team, "the Egyptians were probably aware of this handy trick."