Early thinkers, especially those of pre-Hellenic and early classical Greece, devised the concept of cyclical world history, which, because it postulated a succession of different ages, again involved the idea of great spans of time. These, though of vague durations, were usually stated in terms indicating an antiquity far greater than the 1,656 and 2,342 year dates obtained by biblical studies. This doctrine was followed by, and probably led to the development of, that of the cyclical Great Year, championed by Empedocles and the Pythagorean philosophers of ancient Greece. The doctrine itself was apparently based upon earlier Chaldean teachings which advocated that the Universe, though eternal, undergoes cyclical destruction from either fire or water at lengthy but irregular intervals.