Spatio-temporal analysis of the Indus urbanization

The greater Indus valley was home to Neolithic cultures starting from 7000 BCE. They formed the antecedents of the urban Harappan civilization, whose rise and decline are dated to 2600 BCE and 1900 BCE respectively. At its peak, the Harappan civilization covered an area of more than a million square kilometres, making it the largest urbanized civilization of the Bronze Age. In this communication, we integrate GIS information on topography and hydrology with radio-carbon and archaeological dates of 1874 sites, to analyse the spatio-temporal growth and decline of the Indus urbanization. Our analysis reveals several large-scale patterns in the growth and decline of urbanism. In the growth phase, urbanism appears to nucleate in three distinct geographical locations, situated in Baluchistan, Gujarat and the Ghaggar-Hakra valley. In the mature phase when urbanism is fully developed, the area distribution of sites follows a Zip-fian power law, a feature common to modern urban agglomerations. In the decline phase, the pace of de-urbanization is nonuniform with a strong geographical variation. The decline starts in the Ghaggar-Hakra region, followed by a large-scale collapse in the lower Indus plain, leaving, however, a resilient zone in Gujarat which has a delayed decline. The patterns discerned through our analysis will find use within a Bayesian framework to test hypotheses for the growth and decline of the Harappan civilization.