What did the Greeks think about how the universe began?

The ancient Greeks had various philosophical and mythological ideas about the origin of the universe. Many believed in a primordial chaos, from which everything emerged, as described by thinkers like Hesiod in his work "Theogony." Philosophers like Thales and Anaximander proposed that a fundamental substance, such as water or the "apeiron" (infinite), was the source of all things. Additionally, the cosmos was often viewed as a structured and ordered entity, reflecting the belief in a rational and intelligible universe.