Eratosthenes was one of the great thinkers of ancient Greece whose accomplishments included accurately measuring the Earth's circumference and discovering a simple method for finding prime numbers. In addition to his contributions in mathematics, geography, and astronomy, Eratosthenes was a poet, philosopher, and educator whose wide ranging interests served him well as director of the great ancient library at Alexandria. Eratostheneswas nicknamed "Beta" (Greek for two) by some of his contemporaries. This name may refer to his status as second only to Plato in knowledge, or it may also have been a derogatory term used by detractors to indicate that Eratosthenes had not achieved top standing in any discipline of knowledge.

Eratosthenes was born circa 285 B.C. in Cyrene, which is now Libya, in northern Africa. His father's name was Aglaus, but little else is known about his family or its station in Greek society. At that time...