Neolithic cultures flourished in the greater Indus valley over a period of about 5000 years, starting from 7000 BCE. They formed the antecedents of the urban Harappan civilisation, whose rise and decline are dated to 2600 BCE and 1900 BCE, respectively. At its peak, the Harappan civilisation covered an area of more than a million square kilometers, making it the largest urbanised civilisation of the Bronze age. In this paper, we integrate GIS information on topography and hydrology with radiocarbon and archaeological dates of 1874 sites, to analyse the spatio-temporal growth and decline of the Harappan urbanisation. Our analysis reveals several large-scale patterns in the growth and decay of urbanism. In the growth phase, urbanism appears to nucleate from 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 Zipfian power law, a feature common to modern urban agglomerations. In the decline phase, the pace of de-urbanisation is non-uniform with strong geographical variation. The decline starts in the Ghaggar-Hakra valley, followed by a large-scale collapse in the lower Indus plain, leaving, however, a resilient zone in Gujarat which has a postponed decline. We hope similar quantitative approaches in analysing archaeological data will be useful in testing hypotheses for the growth and decline of the Harappan civilisation.
The movie below shows a summary of the spatio-temporal evolution, sampled at a notional 100 years. It is best viewed in full-screen resolution.