Hypatia was the first woman known to have made a significant contribution to mathematics; she probably occupied the chair of neo-Platonic philosophy at Alexandria. Although there is no evidence that Hypatia did any original research, she assisted her father, Theon of Alexandria, in writing his eleven-part commentary on Ptolemy's great work on astronomy and mathematics, the Almagest. It's thought that she also helped in producing a new version of Euclid's Elements, which formed the basis for all later editions of Euclid. Hypatia became head of the Platonist school at Alexandria in about AD 400 and, as a pagan, represented a threat to some Christian sects who felt threatened by her learning and depth of scientific knowledge. In the end, although the exact circumstances are unclear, she was murdered by a mob. The event served as a trigger for the departure of many scholars and the beginning of the decline of Alexandria as a major academic center.