Complex sentence: The earliest proto-urban settlements with several thousand inhabitants emerge in the Neolithic, while the first cities to house several tens of thousands were Memphis and Uruk, by the 31st century BC (see Historical urban community sizes).
Split into simpler sentences: The earliest proto-urban settlements with several thousand inhabitants emerged in the Neolithic. The first cities to house several tens of thousands were Memphis and Uruk, by the 31st century BC (see Historical urban community sizes).