European philosophy began with a philosophy of nature. At the turn of the sixth centuries bc, on the Ionian coast of Asia Minor, and then in Magna Graecia and Sicily, some dozen or so thinkers dared to try to understand the world using only their own powers, without recourse to religious beliefs. The attempt exceeded all expectations: not with respect to success in understanding, but with respect to a certain kind of chain reaction that could not be stopped. Thus began one of the greatest of human adventures—the process of coming to understand the world by means of thought and experience.