<P> 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). </P> <P> Historic times are marked apart from prehistoric times when "records of the past begin to be kept for the benefit of future generations"; which may be in written or oral form . If the rise of civilization is taken to coincide with the development of writing out of proto - writing, the Near Eastern Chalcolithic, the transitional period between the Neolithic and the Bronze Age during the 4th millennium BC, and the development of proto - writing in Harappa in the Indus Valley of South Asia around 3300 BC are the earliest incidences, followed by Chinese proto - writing evolving into the oracle bone script, and again by the emergence of Mesoamerican writing systems from about 2000 BC . </P> <P> In the absence of written documents, most aspects of the rise of early civilizations are contained in archaeological assessments that document the development of formal institutions and the material culture . A "civilized" way of life is ultimately linked to conditions coming almost exclusively from intensive agriculture . Gordon Childe defined the development of civilization as the result of two successive revolutions: the Neolithic Revolution, triggering the development of settled communities, and the Urban Revolution, which enhanced tendencies towards dense settlements, specialized occupational groups, social classes, exploitation of surpluses, monumental public buildings and writing . Few of those conditions, however, are unchallenged by the records: dense settlements were not attested in Egypt's Old Kingdom and were absent in the Maya area; the Incas lacked writing altogether; and often monumental architecture preceded any indication of village settlement . For instance, in present - day Louisiana, researchers have determined that cultures that were primarily nomadic organized over generations to build earthwork mounds at seasonal settlements as early as 3400 BC . Rather than a succession of events and preconditions, the rise of civilization could equally be hypothesized as an accelerated process that started with incipient agriculture and culminated in the Oriental Bronze Age . </P> <P> A traditional theory of the spread of civilization is that it began in the Fertile Crescent and spread out from there by influence . Scholars more generally now believe that civilizations arose independently at several locations in both hemispheres . They have observed that sociocultural developments occurred along different timeframes . "Sedentary" and "nomadic" communities continued to interact considerably; they were not strictly divided among widely different cultural groups . The concept of a cradle of civilization has a focus where the inhabitants came to build cities, to create writing systems, to experiment in techniques for making pottery and using metals, to domesticate animals, and to develop complex social structures involving class systems . </P>

Where did the earliest civilizations emerge why there