Decline of the Indus cities

What happened

From about 1900 BCE the characteristic features of the urban phase disappear: the script goes out of use, weights and seals cease to be made, long-distance trade contracts, brick standardisation lapses and the large cities are abandoned or shrink drastically.

Occupation does not end. Settlement continues in altered form, shifting eastward towards the Ganges-Yamuna region and persisting in Gujarat, with regional cultures — Cemetery H in the Punjab, Jhukar in Sindh, Rangpur in Gujarat — succeeding the urban phase. What ends is the integrated urban system, not the population.

Explanations

Mortimer Wheeler's mid-century proposal of destruction by Aryan invaders, based on unburied skeletons at Mohenjo-daro, in ancient India (modern-day Pakistan), and Rigvedic references to the destruction of forts, has been abandoned. The skeletons are from different levels and show no evidence of a massacre; no destruction layer has been found; and the chronology does not support it.

Current explanations are environmental and economic. Palaeoclimatic work indicates a weakening of the monsoon around 2200-2000 BCE, part of a wider episode of aridification affecting the Near East. Hydrological change — the drying of the Ghaggar-Hakra system, on which a large concentration of settlements depended, and shifts in the course of the Indus — would have removed the basis for agriculture across whole regions. The contraction of Mesopotamian demand would have undercut the long-distance trade.

Interpretation

The current view is that these acted together over centuries, with different regions failing at different times and for different reasons, and that populations moved rather than perished. The eastward shift towards better-watered land fits the pattern.

What is not explained is why the urban institutions themselves — the script, the weights, the seals — were not carried into the successor cultures. A dispersed population might be expected to retain some of them, and their complete disappearance suggests that whatever sustained them was tied to the cities specifically.