The Greek natural philosopher and astronomer Anaximander (611 BC-ca. 546 BC) attempted to explain the origins of the universe through his theory of the apeiron.

Born in Miletus, Anaximander was the son of Praxiades. According to tradition, he was a pupil of the Greek philosopher Thales. Anaximander is said to have taken part in the founding of Apollonia on the Black Sea and to have traveled to Sparta. His book, On Nature, a title given by Alexandrian scholars to many works of its type, was still in use some 2 centuries after his death.

Anaximander was concerned with the origin of things. He found an explanation, having abandoned with Thales the old mythological cosmogonies, in his theory of the apeiron (the infinite)--that is, the universe is boundless and formless but is constituted of a single primary substance out of which all individual phenomena arise. This concept is similar in some...