Well I'll be darned, here's another hint at circa 2200 BC.
Blam, have you ever seen any pics of the British "hill-forts", particularly the big ones that involved moving one hell of a lot of dirt? Some years back I hypothesized that they might be some kind of refuges for local populations against encroachment from the sea. I also believe that one of the reasons for ancient interest in the heavens was that they KNEW from experience that violent death from above was always a threat.