Theon of Alexandria Theon of Alexandria Theon of Alexandria (; ; 335 – c. 405) was a Greek scholar and mathematician who lived in Alexandria, Egypt. He edited and arranged Euclid's "Elements" and wrote commentaries on works by Euclid and Ptolemy. His daughter Hypatia also won fame as a mathematician. Little is known about the life of Theon. He made predictions and observances of solar and lunar eclipses in 364 which show he was active at that time, and he is said to have lived during the reign of Theodosius I (379–395). The biographical tradition of the tenth century Byzantine "Suda" defines Theon
Library of Alexandria the "Letter of Aristeas" is very late and it contains information that is now known to be inaccurate. Other sources claim that the Library was instead created under the reign of Ptolemy I's son Ptolemy II Philadelphus (283–246 BC). Modern scholars agree that, while it is possible that Ptolemy I may have laid the groundwork for the Library, it probably did not come into being as a physical institution until the reign of Ptolemy II. By that time, Demetrius of Phalerum had fallen out of favor with the Ptolemaic court and could not, therefore, have had any role in establishing