He noted that the Sun's rays fell vertically at noon in Syene (now Aswan), Egypt,

It was down a well that he noticed. I have seen a picture of the well, 50 metres in diameter maybe.

And he was a percent or so out on the polar I think. More on equitorial obviously. But that all depends on your definition of a Greek mile. They knew the moon was spherical, so why not the Earth?

Amazing given the technology available. But I would submit not amazing that there were clever people alive then. In fact looking at who rules our countries today .........................