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It suggests that their response to the perennial nomad raids was to flee to the hills, not hunker in place. Said villages feature many innovative ways of hiding granaries!
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Why does the answer need to involve wheels at all? There was another change that took place starting ~3500 BC: The Bronze Age.
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Also, wheels greatly simplified feeding the large concentrated workforce needed to do the building.
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Per Dr. Hallpike, I'd be more inclined to say natural geographic barriers acted as walls for the locals. If you were of a conquering bent, you eradicated everyone else up to your natural borders.
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