The pyramids are some of the most impressive human-built structures anywhere on the planet - but they're also rather mysterious.
Even with modern technology, they'd be a real feat of construction - so how on Earth did the ancient Egyptians manage it?
Back when many of them were built, no modern tech existed, and the exact mechanics that the Egyptians used to move the vast quantities of rock has long been a topic of fierce debate.
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There's little doubt that it involved huge quantities of human laborers, many of them doubtless slaves, but it's still left historians and scientists scratching their chins.
It turns out that one small wall painting might hold the key to all this, as explored by a team from the University of Amsterdam in 2014.
The painting was from the tomb of an eminent local governor called Djehutihotep, and showed nearly 200 men moving a great sledge with a statue tied to it, something that looks like a pretty brute-force method at first.
However, if you take a closer look, each line of men dragging a rope starts with one figure pouring water onto the ground in front of the procession.
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Curious about this small but very deliberate detail, the team of researchers did a series of tests to see how water poured onto sand changed the amount of force needed to pull a sledge. Amazingly, after some experimentation to decide how much water was needed, they found that it could massively reduce the amount of force required.
In some cases, there was a 50% reduction in the force needed to pull on wet sand compared to dry sand. That means this might have solved one of the great mysteries of how the pyramids were built without simply massive armies of laborers - by using this technique to make sledges move more easily.
Dr Daniel Bonn, who led the research team, told Live Science: "It turns out that wetting Egyptian desert sand can reduce the friction by quite a bit, which implies you need only half of the people to pull a sledge on wet sand, compared to dry sand."
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The best part of this discovery is that it isn't a total solution to every question - it gives us more context and information about how the Egyptians worked, but still leaves plenty of other blank spots to be filled in.
After all, once you drag a giant block of stone to the foot of an in-progress pyramid at Giza, say, you've still got to find a way to get it to the top of the construction. So, levers and cranes and pulleys are very much still potentially part of the equation - there are plenty more exciting revelations yet to be discovered.