The pyramids aren't just old, they're really really old: We are closer in time to Cleopatra than she was to the building of the first pyramids. That mind-boggling time-chasm might explain why the pyramids have proved to be a source of fascination and speculation for modern humans, who can't imagine how our ancient forefathers got anything done without technology, let alone building structures large enough to be seen from space.
Stacking the blocks into the towering iconic shape is often marveled at as a feat of mystery, but just assembling the necessary materials is equally miraculous.
For the Great Pyramid of Giza—which is thought to have been built over a span of two decades for fourth dynasty pharaoh Khufu—over 2,300,000 giant blocks of limestone and granite weighing an average of two and a half tons had to be transported to the site from quarries—some from places like Aswan, more than 500 miles away.
Archeological evidence suggests that the ancient Egyptians used crude wooden sleds to transport the heavy building blocks. But if you've ever dragged something through the sand, you can understand why these sleds might not have eased this task. The weight of the blocks would cause the sled to sink slightly and, as you dragged them, sand would accumulate in front of the sled, increasing the resistance.
A recent study in the journal Physical Review Letters proposes an explanation for how the Egyptians made use of the sleds that is based on a principle most people are familiar with: While dry sand is easily pushed around, wet sand is malleable but more rigid. This is why you need moist sand to give your sandcastles structural integrity at the beach. The correct ratio of water to sand—which is variable, but typically between 2 percent and 5 percent of the volume of sand—causes the water droplets to create capillary bridges that bind the individual grains of sand into a smoother, stronger surface.
In experiments, the force required to pull sleds across sand was reduced by a full 50 percent when the right amount of water was added. Not only would it make sense for the ancient Egyptians to have utilized this tactic, there's evidence to suggest that they did. A wall painting from the tomb of Djehutihotep shows a hoard of workers moving a statue of the Upper Egypt nomarch on a sled. While rows of workers are shown heaving heavy ropes attached to the statue, a single figure is painted perched atop the sled pouring what could certainly be water on to the ground in front of him.
"In fact, Egyptologists had been interpreting the water as part of a purification ritual, and had never sought a scientific explanation," Daniel Bonn, who led the study, told the Washington Post.
The science is sound, but that doesn't necessarily mean it overrules the Egyptologists' theories about Djehutihotep's wall painting or that it applies to the pyramids, which were built over 600 years before Djehutihotep lived. Most reports of the study have assumed that applying their findings to the pyramids is something of a foregone conclusion. Adding water to the sand to decrease friction certainly makes sense, but that doesn't necessarily mean it's what the Egyptians did.