6th millennium BC, interesting indeed. I am a proponent of Graham Hancock, Robert Schoch, etc. theories that have long posed that an advanced civilization(s) existed during the last Ice Age, roughly 12.8K to 11.6K years ago that then got wiped out by a global cataclysm (both Hancock and Schoch have differing views on how that advanced civilization end global cataclysmic wise but both agree that an advanced civilization(s) existed up to that point).
At any rate, as they keep digging, so to speak, they are going to find that civilization existed long before academia has long taught and postulated.
I wonder if it was the Flood?
Gobekli Teppe proves that quite nicely. Site dates to 12,000 years ago.