Anaximander (in Ancient Greek Ἀναξίμανδρος; Miletus, Ionia; c. 610 BC - c. 545 BC) was a philosopher and geographer of Ancient Greece. Disciple and follower of Thales, and companion and teacher of Anaximenes, considered that the principle of all things (arché) is the apeiron. He is credited with just one book, known as On Nature. The book has been lost and its word has arrived at the present time through doxographic commentaries of other authors. He is also credited with a terrestrial chart, the measurement of the solstices and equinoxes by means of a gnomon, works to determine the distance and size of the stars and the affirmation that the Earth is cylindrical and occupies the center of the universe.