Parallel (geometry) as a pair of straight lines in a plane which do not meet appears as Definition 23 in Book I of Euclid's Elements. Alternative definitions were discussed by other Greeks, often as part of an attempt to prove the parallel postulate. Proclus attributes a definition of parallel lines as equidistant lines to Posidonius and quotes Geminus in a similar vein. Simplicius also mentions Posidonius' definition as well as its modification by the philosopher Aganis. At the end of the nineteenth century, in England, Euclid's Elements was still the standard textbook in secondary schools. The traditional treatment of geometry was being
Library of Alexandria BC, however, Aristarchus became caught up in a dynastic struggle in which he supported Ptolemy VII Neos Philopator as the ruler of Egypt. Ptolemy VII was murdered and succeeded by Ptolemy VIII Physcon, who immediately set about punishing all those who had supported his predecessor, forcing Aristarchus to flee Egypt and take refuge on the island of Cyprus, where he died shortly thereafter. Ptolemy VIII expelled all foreign scholars from Alexandria, forcing them to disperse across the Eastern Mediterranean. Ptolemy VIII Physcon's expulsion of the scholars from Alexandria brought about a shift in the history of Hellenistic scholarship. The scholars