Born around 276 B.C. in Cyrene, Libya, Eratosthenes soon became one of the most famous mathematicians of his time. He is best known for making the first recorded measurement of the Earth’s circumference, which was also remarkably accurate. (And, yes, people at that point had known for some time that the world wasn’t flat, contrary to popular belief .) Read more…        

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How the Circumference of Earth Was Accurately Estimated 2000 Years Ago