Listen to part of a lecture in an archaeology class.
Professor: The Great Pyramid of Giza in Egypt might be the most famous building in the world.
We know exactly when it was built.
Construction started in 2547 B.C.E., about 4500 years ago.
We know who had it built.
That was the pharaoh Khufu.
And we know who oversaw its construction—the pharaoh's brother.
We know so many things about it, but the funny thing is: we still don't know exactly how it was built.
This picture will give you an idea of the size of the Pyramid and the size of the blocks it's made out of.
About two million stone blocks were used to build the Great Pyramid and they are incredibly massive.
The average weight is two and a half tons.
The problem that has puzzled scholars for centuries is how were these blocks lifted up the height of this massive structure and then fit into place and without the benefit of modern technology.
Of course, there've been a lot of theories over the centuries.
The oldest recorded one is by the Greek historian Herodotus.
He visited Egypt around 450 B.C.E. , when the Pyramid was already 2000 years old.
His theory was that cranes were used, much like we use cranes today to construct tall buildings.
And Herodotus may have seen Egyptians using cranes made of wood.
But the problem with this theory has to do with simple mechanics.
A crane needs a wide and sturdy base to stand on or it will fall over.
Well, as you get toward the top of the Pyramid, there's really no place for a crane to stand.
The stone blocks are too narrow to provide a base.
Well, so much for that theory.
The next one has to do with the use of a ramp that would allow workers to drag a stone block up the side of the structure.
Of course the ramp can't be too steep.
It has to have a long gentle slope. And that's the problem.
If you build a ramp with a slight slope up to the top of a Pyramid that's over 130 meters high, it would have to be almost two kilometers long.
Well, the Pyramid is built on a flat area called the Giza Plateau.
The Plateau is simply not big enough to accommodate a two-kilometer-long ramp.
OK. So what now?
Well, if you've ever driven on a mountain road, you'd know that it has a lot of twists and turns and bends in it because that's how engineers keep the road from having to be too steep.
So why not wrap the ramp around the Pyramid?
Building the ramp around it as you go.
Sounds like a pretty good idea.
Except it's got a serious problem.
See...one of the most remarkable things about the Great Pyramid is how accurate the proportions are.
The dimensions are almost perfect.