"Since the classical Greeks already, it has been common to date Zarathuštra to the 6th century BC, hardly a few generations before the Persian wars. In popular literature, this date is still given, but scholars have now settled for an earlier date: “The archaism of the Gāthās would incline us to situate Zarathuštra in the very beginning of the first millennium BCE, if not even earlier.” (Varenne 2006) But how much earlier? According to leading scholar SkjaervØ, “Zoroastrianism (…) originated some four millennia ago”."