When studying monuments like Stonehenge it becomes clear (or at least seems probable) that the ancients knew what the size of the earth was.

This becomes even more evident when reading books like these.

But how did they figure it out?

And why hasn't anyone ever seriously tried to answer that question? Or even ask it?

Did they think it was impossible or unlikely?

Well, it seems it wasn't. In fact it's quite easy. All you need is a lot of time and some manpower (or was it the other way around?).

But let's not spoil the surprise by just telling you outright. Let's see if you can find out for yourself how the earth was measured some 3000 years B.C.

So let's suppose it's 3000 B.C.
You are in England.
You have no boat.
You want to know the size of the planet you're on.

Where do you start?

By realising that we are not on the Tropic of Cancer like what the Gyppoes are so we can't use Eratosthenes' simple trick of peering down a well to know when (and where) the sun is overhead at midday at mid-summer.

Exactly. So we have to find ourselves an equivalent of a well (so to speak). Because then we have prerequisite A, which is ....

Keimpe wrote:When studying monuments like Stonehenge it becomes clear (or at least seems probable) that the ancients knew what the size of the earth was.

This becomes even more evident when reading books like these.

But how did they figure it out?

Have you figured it out yet?
(I have) ;-)