Philosophy began in Ionia at the end of the 7th century BCE and combined ancient Greek mythology with rational thought to explain the forces which compose nature. The foundation of the Ionian school in Miletos was the starting point for an early philosophy in which the ancient Greek gods were considered in charge of, but were not equal to, the natural forces. Philosophy described a world composed of laws and principles and introduced physics, an idea which inspired the legal concept of the polis.