Anaximander

Anaximander used the idea of the apeiron, often translated as the boundless or indefinite, as the origin of things. This was a major step in early Greek philosophy because it explained nature without relying only on mythic genealogy.

Yes, Anaximander was part of the Milesian school, the same early Greek tradition associated with Thales. He lived in the 6th century BCE in Miletus, a Greek city in Ionia.

Ancient sources credit Anaximander with making an early Greek map of the known world. Whether the exact map survived is another matter, but the attribution shows his reputation for geography and cosmology.

Anaximander is reported to have argued that Earth stays in place without needing support because it is balanced in relation to everything around it. That idea was strikingly abstract compared with older images of Earth resting on something.