The Ionian school of Pre-Socratic philosophy refers to Ancient Greek philosophers, or a school of thought, in Ionia in the 6th century B.C, the first in the Western tradition. The Ionian School included such thinkers as Thales, Anaximander, Anaximenes, Heraclitus, Anaxagoras, and Archelaus. This classification can be traced to the doxographer Sotion. The doxographer Diogenes Laërtius divides pre Socratic philosophy into the Ionian and Italian School. The collective affinity of the Ionians was first acknowledged by Aristotle who called them physiologoi (φυσιολόγοι), or natural philosophers. They are sometimes referred to as cosmologists, since they studied stars and maths, gave cosmogonies and were largely physicalists who tried to explain the nature of matter. The first three philosophers (Thales, Anaximander, and Anaximenes) were all centred in the mercantile city of Miletus on the Maeander River and are collectively referred to as the Milesian School. They sought to explain nature by finding its fundamental element called the arche. They seemed to think although matter could change from one form to another, all matter had something in common which did not change. They were thus characterized by Aristotle as material monists. They also believed all was alive, or were hylozoists. The Milesians did not agree on what all things had in common, and did not seem to experiment to find out, but used abstract reasoning rather than religion or mythology to explain themselves, and are thus credited as the first philosophers. Thales Thales (Greek: Θαλῆς, Thalēs) of Miletus (c. 624 – c. 546 BCE) is regarded as the earliest Western philosopher. Before him, the Greeks explained the origin and nature of the world through myths of anthropomorphic gods and heroes. Phenomena like lightning and earthquakes were attributed to actions of the gods. By contrast, Thales attempted to find naturalistic explanations of the world, without reference to the supernatural. He explained earthquakes by imagining that the Earth floats on water, and that earthquakes occur when the Earth is rocked by waves.