In ancient Babylonia, famed for its astrology, there were not separate roles for the astronomer as predictor of celestial phenomena, and the astrologer as their interpreter; both functions were performed by the same person. This overlap does not mean that astrology and astronomy were always regarded as one and the same. In ancient Greece, pre-Socratic thinkers such as Anaximander, Xenophanes, Anaximenes, and Heraclides speculated about the nature and substance of the stars and planets.