Ancient philosophy, the basis of Western thought and science, evolved in the course of almost one thousand years. In the sixth century BC that process was begun in which we still find ourselves: the attempt at a rational explanation of the world and of man's place in the world. The earliest period until just past the middle of the fifth century BC was economically, socially and politically a period of crises, but at the same time a period which opened up for foreign influences provoking thinkers and poets to seek for some order behind all changes, an order that could be grasped by human thought. They brought earlier thought to a conclusion, created a conceptual apparatus that has left its impress on all subsequent Western philosophy, and assigned man a place in society and the cosmos at the moment when the era of greatness had been lost irretrievably, and the city state was in decay. Still, new philosophical systems were formulated- Epicureanism and Stoicism - and philosophy was still a universal explanation of the world; but the emphasis was on ethics, and it was in this period that philosophy and science began to pursue their own paths.