I saw the Great Pyramid of Giza in Egypt. It's literally just large stacked stones. Nothing holding them together but gravity.

(Also, the pyramids are right next to the city of Giza. Every photo makes them look like some exotic ruins deep in the desert, but there's literally modern civilization and plant life everywhere, if you turn the camera in pretty much any other direction.)

I toured some smaller pyramids further out in the desert. Some of them had literally started to collapse because they weren't built with perfectly shaped stones, or the thousand of years of weathering had worn them away until they didn't sit evenly anymore and slid off their base.

The Great Pyramid of Giza is only still standing because the stones are absolutely massive. They probably need another million years or so before they're eroded enough to start collapsing.

Interestingly enough, the original Great Pyramid of Giza was covered with a solid, smooth, white limestone outer shell, with a gold cap at the top. You could technically slide all the way down its sides, no steps to climb up or anything.

But people have plundered and looted so much over the past thousands of years before we started preserving them, that all that's left is the ragged, rough underside of the pyramid. The entire outer shell is long gone.

To be fair, it did take them a long time to get it right. It seems simple, but it's actually surprisingly difficult.

https://architecturecompetitions.com/the-evolution-of-the-egyptian-pyramids