# How the Pyramids Were Built (Pyramid Science Part 2!)

This episode is supported by Skillshare. Hey smart people, so a few weeks ago we made a video about the pyramids, and how, while they are pretty heckin’ impressive, we can trace the evolution of their construction and see the ancient Egyptians using trial and error, and even making a few mistakes, which basically tells us they didn’t need aliens to build them, they just needed science. You guys really liked that video, but a few of you were… a little bothered that, despite the fact it was called “WHO built the pyramids?” that I didn’t talk about HOW the pyramids were made. Soooo, let’s talk about it! [OPEN] The hundred-plus pyramids scattered around Egypt were all built a bit differently, but we’re gonna focus on THE BIG ONE. Let’s review the stats! The Great Pyramid originally rose more than 146 meters tall and contained about 2.3 million stone blocks.

But the start of any construction project truly begins with the foundation, which is impressive in its own right. Its base is level to less than 2 cm, it’s square to within 11 (cm), and its edges are aligned to the compass within 3/60ths of a degree. This precision is pretty incredible since compasses didn’t actually exist yet, and since forty-five hundred years ago the North Star was in a completely different place. But finding North is actually pretty easy, just watch where any star rises and sets during the night, and cut the angle in half. After that, squaring the sides just requires measuring a right angle. Pythagoras and his equation came way later, but ancient cultures like the Egyptians knew a 3-4-5 triangle made a 90˚ corner.

They could even make a right angle with two circles: the line connecting the intersection of the arcs is perpendicular to a line through their centers. To level the base, some theories say the Egyptians used water filled channels as natural levels, but this isn’t likely when you consider how much water they’d have to carry in to keep it from evaporating. But if you can make a right angle, you can make a level. Put that on some legs, and you can level over long distances. When you think about it, a pyramid is just a bunch of stacked squares, so if you can master this measurement, you’re most of the way there. Now we just need some stones. The Great Pyramid’s core is made of more than 2 million blocks of rough yellow limestone.

This was quarried right next to the pyramids, which is a big reason why they chose sites like Giza, where prehistoric oceans had deposited this building material right under their feet. They would dig channels and pry these blocks right from the Earth, and the size of the blocks was actually determined by the natural thickness of these limestone layers. You can see evidence of these layers in The Sphinx, which was actually dug out of the Earth, not built on top of it. The pyramids were originally covered in smooth white limestone from quarries up the Nile, which was stolen to use in other buildings thousands of years ago. We’ve found many chisels, drills, and saws used at these quarries, and the only metal Egyptians had access to was copper.

That’s a pretty soft metal, but when a slurry of sand and powdered rock is poured in as an abrasive, even copper tools can cut limestone. To build the Great Pyramid in 23 years, an Olympic swimming pool’s worth of stone had to be quarried every eight days. That’s a lot, but modern pyramid building experiments using technology available to Ancient Egyptians calculated this amount of stone could be cut and moved by a quarry team of 1200 to 1500 workers, which is totally doable. Heavier stones, like the granite used in the pyramid’s inner chambers, are much harder than limestone. They were literally chipped out by hand using heavy dolerite hammer stones, which we’ve also found… a LOT of. It would have taken a full day’s pounding to chip away a few centimeters, but then again they didn’t have Twitter to distract them. We’ve found Egyptian boats large enough to have floated these stones down the Nile, but how were 2 million blocks actually moved into place?

It might be hard to believe, but wheels for transportation are a surprisingly recent invention. Not because rolling a round thing is hard to figure out but because inventing a workable axle is. The oldest known rolling wheels on Earth date to before the Great Pyramid, but not in Egypt. Paintings tell us Egyptians used wooden sleds to move large objects, but they still had to deal with friction. Burying wood rails horizontally will allow a sled to slide more freely, but researchers at the University of Amsterdam showed in 2014 that sand has an interesting property, wetting it with the right amount of water makes it remarkably slick. A team of ten workers can easily pull a one-ton sled, but people always seem to forget that Egyptians had animals like donkeys and cattle around to help too. Constructing ramps to deliver stone must have been nearly as monumental as the pyramid itself.

This is one place where there’s no records of what they looked like, but researchers have examined lots of possibilities. An engineer named Craig Smith has done probably the most detailed ramp analysis, calculating how many stones could be delivered with each design, and he believes the Egyptians extended a big, wide ramp near the bottom where a pyramid requires most of its stones, and spiral ramps near the top where fewer blocks are needed. Wooden levers, and round dolerite “ball bearings” were used to guide stones into place, where they were carved to an exact fit. Joints between some of the few remaining smooth outer stones are so precise you can’t even slip a credit card between them, but digs have shown they weren’t as careful with interior stones. It’s a popular idea that the pyramids were built by slaves, but you shouldn’t believe everything you see in the movies.

Egyptologists like Mark Lehner have uncovered enormous cities built to feed, house, and equip thousands of skilled workers, with breweries, bakeries, tool shops… signs that whole families lived nearby. Egyptian society at all levels dedicated themselves to what they viewed as the kingdom’s proudest work. It’s actually pretty incredible that we have as much evidence as we DO about how the pyramids were built, but that doesn’t mean building them was easy. In fact it’s the opposite. But difficult doesn’t mean impossible