<P> Anaximander (/ æˌnæksɪˈmændər /; Greek: Ἀναξίμανδρος Anaximandros; c. 610--c. 546 BC) was a pre-Socratic Greek philosopher who lived in Miletus, a city of Ionia (in modern - day Turkey). He belonged to the Milesian school and learned the teachings of his master Thales . He succeeded Thales and became the second master of that school where he counted Anaximenes and, arguably, Pythagoras amongst his pupils . </P> <P> Little of his life and work is known today . According to available historical documents, he is the first philosopher known to have written down his studies, although only one fragment of his work remains . Fragmentary testimonies found in documents after his death provide a portrait of the man . </P> <P> He was an early proponent of science and tried to observe and explain different aspects of the universe, with a particular interest in its origins, claiming that nature is ruled by laws, just like human societies, and anything that disturbs the balance of nature does not last long . Like many thinkers of his time, Anaximander's philosophy included contributions to many disciplines . In astronomy, he attempted to describe the mechanics of celestial bodies in relation to the Earth . In physics, his postulation that the indefinite (or apeiron) was the source of all things led Greek philosophy to a new level of conceptual abstraction . His knowledge of geometry allowed him to introduce the gnomon in Greece . He created a map of the world that contributed greatly to the advancement of geography . He was also involved in the politics of Miletus and was sent as a leader to one of its colonies . </P> <P> Anaximander, son of Praxiades, was born in the third year of the 42nd Olympiad (610 BC). According to Apollodorus of Athens, Greek grammarian of the 2nd century BC, he was sixty - four years old during the second year of the 58th Olympiad (547--546 BC), and died shortly afterwards . </P>

Who proposed the indefinite as the structure of reality