Eratosthenes (C. 276 BCE - C.194 BCE)
Greek astronomer, geographer, philosopher and mathematician who, at 30 years of age, was appointed chief librarian of the Library of Alexandria by the pharaoh Ptolemy III.
Eratosthenes (c. 276 BCE – c. 194 BCE)
He is credited with having calculated the circumference of the Earth with an error of less than 1%, which is quite accurate for his time. He also developed a method called the "sieve of Eratosthenes" to determine the sequence of prime numbers.