Eucli (Greek: Εὐκλείδης — Eukleidēs), fl. 300 BC, also known as Euclid of Alexandria and the "Father of Geometry", was a Greek mathematician of the Hellenistic period who was active in Alexandria, almost certainly during the reign of Ptolemy I (323 BC–283 BC). His Elements is the most successful textbook in the history of mathematics. In it, the principles of what is now called Euclidean geometry are deduced from a small set of axioms. Euclid also wrote works on perspective, conic sections, spherical geometry, and rigor.