Decline of the Indus Valley Civilization

The event

Beginning around 1900 BC, the great Indus cities entered a long, uneven decline. Populations at Mohenjo-daro and Harappa dwindled, the meticulous urban planning that had marked the civilization's peak broke down, its distinctive script fell out of use, and the long-distance trade that had once carried Indus goods to Mesopotamia dried up.

The older idea that invading Indo-Aryan warriors violently overthrew these cities has largely given way, in current scholarship, to environmental explanations: shifting river courses (including the drying of a river system many cities relied on) and a weakening of the monsoon rains that had sustained the agricultural surplus a large urban population required. At most sites, there is little evidence of warfare or sudden violent destruction — the picture is one of quiet, gradual abandonment rather than conquest.

It is a sober reminder that even the most advanced human achievements rest on foundations — rivers, rainfall, seasons — that belong to God alone to sustain or withhold. 'Vanity of vanities... all is vanity,' the Preacher writes of every human work done 'under the sun' (Ecclesiastes 1:2), and a civilization as advanced as any of its day, forgotten so completely that it lay unknown until its rediscovery in the 1920s, illustrates the point as well as anything in the ancient world.

Dating

Older scholarship attributed the decline to an 'Aryan invasion,' partly on outdated readings of the Rigveda. Most archaeologists today instead point to climate change, a weakening monsoon, and the drying up of the Sarasvati/Ghaggar-Hakra river system that many of the cities depended on. The pace is also debated — some sites were abandoned abruptly, others faded gradually over generations.