Anaximander (circa 611-c. 547 bc), Greek philosopher, mathematician, and astronomer, born in Miletus in what is now Turkey. He was a disciple and friend of the Greek philosopher Thales. Anaximander is said to have discovered the obliquity of the ecliptic, that is, the angle at which the plane of the ecliptic is inclined to the celestial equator. He is credited with introducing the sundial into Greece and with inventing cartography. Anaximander's outstanding contribution was his authorship of the earliest prose work concerning the cosmos and the origins of life. He conceived of the universe as a number of concentric cylinders, of which the outermost is the sun, the middle is the moon, and the innermost is the stars. Within these cylinders is the earth, unsupported and drum-shaped. Anaximander postulated the origin of the universe as the result of the separation of opposites from the primordial material. Hot moved outward, separating from cold, and then dry from wet. Further, Anaximander held that all things eventually return to the element from which they originated.