wetlands and floodplain cultures do not leave a strong archaeological record, so by the time evidence begins to emerge of a city in a former wetland it may be an image of that settlement in "an already mature phase of urban expansion," a kind of "marsh metropolis"
"in China's Shandong province, on the lower reaches of the Yellow River, settlements of 300 hectares or more--such as Liangchengzhen and Yaowangcheng--were present by no later than 2500 BC, which is over 1000 years before the earliest royal dynasties developed on the Central Chinese plains."
"On the other cide of the Pacific, around the same time, ceremonial centres of great magnitude developed in the valley of Peru's Rio Super, notably at the site of Caral, where archaeologists have uncovered sunken plazas and momumental platforms four millennia older than the Inca empire"
Interestingly, these cities are "much older [...] than the systems of authoritarian government and literate administration that were once assumed necessary for their foundation."
"Similar revelations are emerging from the Maya lowlands, where ceremonial centers of truly enormous size--and, so far, presenting no evidence of monarchy or stratification--can now be dated back as far as 1000 BC: more than 1,000 years before the rise of Classic Maya kings, whose royal cities were notably smaller in scale"