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Eratosthenes expanded the library's holdings, adding a section devoted to of Homer, and original copies of great tragic dramas by Aeschylus, Sophocles and Euripides. They may not have been the only original copies of works that were added to the library. 

The owner of any privately owned text that arrived in Alexandria was required to surrender it to the Library for duplication, if necessary, and the quality of reproduction is said to have meant that it was impossible to tell if the owner had received the original or the library's copy when the volume was returned.

Apart from that calculation and his literary work, Eratosthenes made several significant contributions to mathematics and science. He calculated the Earth's axial tilt, developed the armillary sphere (a celestial globe) around 256 BC, introduced an efficient method to identify prime numbers (the sieve of Eratosthenes), and may have calculated the distance from the Earth to the Sun and the Moon as well as the Sun's diameter. 

He also devised a calendar based on a 365 day year, with every fourth year having an extra 'leap day'.

However, for all that, there was one development that overshadowed the rest. Eratosthenes effectively invented the discipline of geography, including terminology still used today.

His position at the Library of Alexandria gave him access to the accumulated knowledge of the classical world. The collection would have included almost every existing travel book. Their descriptions of the known world, information needed to be pieced together and collated into an organised format.

Eratosthenes did just that in his three-volume Geography (Geographika), which described and mapped the known world, divided the Earth into five climatic zones and gave the names and locations of more than four hundred cities.

© Ian Hughes 2017