Eratosthenes was one of the most versatile scholars of the ancient Greek world. As a mathematician and chief librarian at the Museum of Alexandria, in Egypt, he worked at the center of Greek science. He was the founder of mathematically based geography and was famous for his accurate measurement of Earth's circumference. Eratosthenes, along with his friend Archimedes, Euclid, and other third-century B.C. mathematicians, raised Greek science to unprecedented heights.

Eratosthenes was born in Cyrene, a prosperous Greek city-state in North Africa (modern-day Libya), about 276 B.C., although his birthdate is sometimes placed as early as 285 B.C.. The son of Aglaos, he studied with the grammarian Lysanias in Cyrene and perhaps with the poet Callimachus in Alexandria and Eratosthenes achieved early renown as a poet. He then spent several years in Athens, studying astronomy and geometry with Arcesilaus, and philosophy with Bion the Cynic, Ariston of...