Anaximenes of Miletus (; ; ) was an Ancient Greek, Ionian Pre-Socratic philosopher from Miletus in Asia Minor (modern-day Turkey), active in the latter half of the 6th century BC. The details of his life are obscure because none of his work has been preserved. Anaximenes' ideas are only known today because of comments about him made by later writers, such as Aristotle. As the last of the three philosophers of the Milesian School, considered the first philosophers of the Western world, Anaximenes is best known and identified as a younger friend or student of Anaximander, who was himself taught by the first philosopher Thales. Each developed a distinct cosmology without completely rejecting their predecessors views. Each were material monists who sought to discover the arche; the one, underlying physical yet divine basis of everything. Thales proposed all was made of water; Anaximander proposed all was made of apeiron or something indefinite rather than something specific, and Anaximenes proposed all was made of air, or literally aer which may also include mist or vapor. More condensed air made for colder, denser objects and more rarefied air made for hotter, lighter objects. Much of his astronomical thought was based on Anaximander's, though he altered Anaximander's astrological ideas to better fit his own philosophical views on physics and the natural world. Anaximenes believed the Earth was flat like a disc and rode on air like a frisbee. The Anaximenes crater on the Moon is named in his honor. Some of Anaximenes' writings are referenced during the Hellenistic Age, but no record of these documents currently exist. Apollodorus of Damascus estimated Anaximenes' lifespan as having flourished during the same time period in which Cyrus the Great defeated Croesus at the Battle of Thymbra in 546 BC. Philosophy may have spread elsewhere because Miletus was captured by the Persian army in 494 BC. Air as the Arche Anaximenes thought air was the primary substance that held the universe together. He believed that air was infinite and divine. He was the first to use the word pneuma (“breath of life”) as a synonym for air. One of the only surviving quotes by Anaximenes reads: “Just as our soul...being air holds us together, so pneuma and air encompass [and guard] the whole world.” The analogy compared atmospheric air as the divine and human air as souls that animate people. This relation of the macroscopic and microscopic