Miletus, one of the Greeks’ greatest cities, was located on the western coast of what is now Turkey and was home to where some of the earliest ideas about chemistry were recorded. During the sixth century B.C.E., the Milesian school of thought was founded, and the musings of three philosophers survived into the modern era: Thales, Anaximander, and Anaximenes. Thales thought the most basic building block of the universe was water and that the Earth floated on top of this celestial water. Anaximander challenged both of these ideas, proposing that the universe was born when fire and water (or hot and cold) separated from one another and that the Earth simply floated on nothing. Anaximenes, who was a friend or perhaps student of Anaximander, countered that air was the most basic substance and that air condensed to form water and evaporated to reverse that process.