Eratosthenes

Greek mathematician, geographer, poet, astronomer, librarian and music theorist

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Academics rank#179
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Lived -276–-194, aged 82

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Wikipedia
101 languages
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Era
-276–-194
Aged 82

Summary

Updated 2026-06-08

He measured the planet with a stick and some geometry — no satellites, no instruments beyond shadow and angle — and got Earth's circumference within a few hundred miles. That calculation, done in the third century BC, made him the first person to actually know the size of the world he stood on.

Biography

About

Eratosthenes of Cyrene was born around 276 BC and became chief librarian at the Library of Alexandria, the intellectual center of the ancient world. A polymath who worked across mathematics, astronomy, poetry, and music theory, he coined the term "geography" and built the first global map using parallels and meridians. He calculated Earth's axial tilt with startling precision, founded scientific chronology by dating the fall of Troy to 1184 BC using Egyptian and Persian records, and in number theory introduced the sieve of Eratosthenes for identifying primes. His admirers called him Pentathlos…

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