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Eratosthenes' Map Eratosthenes was another philosopher. He was born in 276 BC in Cyrene, a city in North Africa. For most of his life Eratosthenes worked as a librarian at the famous library in Alexandria, Egypt. Eratosthenes was interested in geometry and prime numbers. He also measured the circumference of the earth. His answer was 250,000 stadia. Unfortunately, we don't know exactly how long one stade was. But we think it was somewhere between 157.2 meters and 166.7 meters. This makes Eratosthenes' measurement somewhere between 39 300 000 meters and 41 675 000 meters. The circumference of the earth is really about 40 000 000 meters, so Eratosthenes' estimate was quite good! Eratosthenes also made a map of the world. He used the same reference lines as Dicaearchus, but he also drew seven parallel lines to each of his defining lines to make a rectangular grid. Eratosthenes' map might have looked something like this: 
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