This major breakthrough has been traced back to the emergence of natural philosophy in 6th century B.C. in the Ionian city of Miletus on the Western coast of Asia Minor.  Miletus was a major trading center with ideas coming in via ships from all over the Mediterranean world. Miletus had the advantage of not being run by a strong political/theological system, so its citizens were mostly free to express their ideas without fear of recriminations from the ruling powers in the city, as had been the case in prior civilizations.