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 (although they could keep records with Quipus); 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.