Ancient Greeks are famous for more than their mythology, e.g. their natural philosophy that laid the foundations of modern science. Greek philosophers challenged theistic explanations of nature early on.
The roots of Western philosophy began in the Greek world in the sixth century BCE. The first Hellenic philosophers were not atheists, but they attempted to explain the world in terms of the processes of nature instead of by mythological accounts. Thus lightning was the result of "wind breaking out and parting the clouds",[49] and earthquakes occurred when "the earth is considerably altered by heating and cooling".[50] The early philosophers often criticized traditional religious notions. Xenophanes (6th century BCE) famously said that if cows and horses had hands, "then horses would draw the forms of gods like horses, and cows like cows".[51] Another philosopher, Anaxagoras (5th century BCE), claimed that the Sun was "a fiery mass, larger than the Peloponnese"; a charge of impiety was brought against him, and he was forced to flee Athens.[52]
The roots of Western philosophy began in the Greek world in the sixth century BCE. The first Hellenic philosophers were not atheists, but they attempted to explain the world in terms of the processes of nature instead of by mythological accounts. Thus lightning was the result of "wind breaking out and parting the clouds",[49] and earthquakes occurred when "the earth is considerably altered by heating and cooling".[50] The early philosophers often criticized traditional religious notions. Xenophanes (6th century BCE) famously said that if cows and horses had hands, "then horses would draw the forms of gods like horses, and cows like cows".[51] Another philosopher, Anaxagoras (5th century BCE), claimed that the Sun was "a fiery mass, larger than the Peloponnese"; a charge of impiety was brought against him, and he was forced to flee Athens.[52]
https://en.wikipedia.org/wiki/History_of_atheism#Philosophy