We have placed the flowering of bronze metallurgy in the context of the Bronze Age city. Let us explore urbanism now.
In general, the settings of our civilizations are the broad expanses of the valleys of great river systems, but due to the needs of irrigation from river floods (the Nile), or short canals/ditches (the Euphrates), or ground water (lift irrigation in South Asia and China), actually it was a series of enclaves in each valley that were populated. Urbanism is possible only when the land has a capacity to support a large number of people per unit area: for it entails the clustering of people in dense settlements, rather than an even dispersal across the landscape. Also necessary are technologies that make feasible the transport of bulky food grain to the non-farming populations of urban nodes.
In Egypt the Nile was the main artery of communication for the narrow valley. The energy of winds and the river current were freely available. In Mesopotamia too, a great deal of transportation was handled along the Euphrates, and city temples employed large numbers of boatmen. The Indus, too, is a navigable river, but here as in Mesopotamia, we also have evidence for the use of wheeled vehicles. And there were pack animals too: the donkey in Egypt and Mesopotamia, oxen in India.
Yet there was nothing inevitable about the growth of cities. City life and clustering makes sense only when there are several persons engaged in diverse non-food producing occupations such as metallurgy, seal carving, administration, serving the temples, trade, etc. (Only such activities benefit from spatial clustering— agriculture does not.)