As the fighters of the Islamic State drive from village to captured village in their looted humvees, they criss-cross what in ancient times was a veritable womb of gods. For millennia, the Fertile Crescent teemed with a bewildering variety of cults and religions. Back in the 3rd Christian century, a philosopher by the name of Bardaisan was so overwhelmed by the sheer array of beliefs to be found in Mesopotamia that he invoked it to disprove the doctrines of astrology.