A later librarian, Eratosthenes (c. 276–196), was a geographer as well as a mathematician. A great friend of Archimedes, he believed that all the earth’s oceans were connected, that Africa might one day be circumnavigated and that India ‘could be reached by sailing westward from Spain’. It was Eratosthenes who calculated the correct duration of a year, who put forward the idea that the earth is round, and calculated its diameter to within an error of fifty miles.
