Thales of Miletus, (624–;546 B.C.), an early Greek philosopher, born in Miletus, Asia Minor. He was the first person known to have attempted to explain the world in nonmythological terms. Thales taught that all substances in the entire world were formed out of one original substance; this original substance he believed to be water. He described the earth as a flat disk floating in water.

Thales is credited with introducing geometry into Greece and with formulating several basic theorems of geometry. He was also an astronomer and is said to have predicted accurately an eclipse of the sun occurring in 585 B.C. Thales' ideas were not written down until long after his death.