[FastCoyote]

So, to have to build fortifications like these, you must be scared witless of being overrun by pretty large forces. No?

[Fred Nerks]

...I have a collection of images of circular and concentric ringed structures, some with standing stones, some with mounds, some with central features, that number in the hundreds; throughout europe, the Sahara, Iran, and South America. I think I even have one from Tibet. I am inclined to believe it was not a defensive layout at all, but, because they are so wide-spread, they may be an imitation of something the people saw, perhaps a celestial phenomenon.

The design is also repeated in rock art, and Stone Henge also follows a similar lay-out.

It does raise the question of population however. How many people worked for how long to raise the structures?

[Fred Nerks]

...for example:

[Citizen Tom Paine]

If they were fortresses, who were they defending against? What might colossus bestrode the world at that time? I read the same question asked about the walls at Jericho? Apparently the non-farmers constantly attacked those that settled and built settlements which the fortified.