# Eratosthenes of Cyrene

**Eratosthenes of Cyrene** (c.275-192): mathematician, geographer, astronomer, social theorist, historian, scholar, librarian in Alexandria.

One of the students of the great poet Callimachus of Cyrene was Eratosthenes of Cyrene (c.275-192 BCE), who became librarian in the Museum, the scientific institute of Alexandria. He invented a new method to calculate prime numbers, drew a famous world map, catalogued several hundreds of stars, but became especially famous for his calculation of the circumference of the earth, based on the angle of the shadow that the sun made over a vertical pole at Alexandria at noon and the fact that at the same time, the sun light fell straight into a well as Syene in southern Egypt. He concluded that the circumference was 45,460 kilometers, which is pretty close to the real figure. (The first modern estimate, by Snellius in 1617, was 38,660 kilometers.)

He also wrote a treatise on chronology and a book on musical theory, composed poems and comedies, and was responsible for two dictionaries and a book on grammar. As an ethnologist, he suggested that the common division between civilized people and barbarians was invalid (text).

Eratosthenes was nicknamed *BĂȘta* or "number two", because in no branch of science he was ever the best, although he excelled in nearly every one of them. The name may refer to the fact that he was from Cyrene, where the inhabitants prided themselves on being "number two" in every field.^{note}

### Literature

- Duane W. Roller, Fragments Collected and Translated, with Commentary and Additional Material (2010) Princeton