HINTS：?

skeptical?

Syene?

Eratosthenes?

Alexandria 800 kilometers?

obelisks

make sense.

An overly skeptical person might have said that the report from Syene was an error, but it's an absolutely straightforward observation. Why would anyone lie on such trivial matter? Eratosthenes asked himself how it could be that at the same moment, a stick in Syene would cast no shadow and a stick in Alexandria 800 kilometers to the north would cast a very definite shadow. Here is a map of ancient Egypt. I have inserted two sticks or obelisks, one up here in Alexandria and one down here in Syene. Now if at a certain moment, each stick casts no shadow, no shadow at all. That's perfectly easy to understand, provided the earth is flat. If the shadow at Syene is at a certain length and the shadow at Alexandria is the same length, they also make sense.

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