SOCIETY × ENVIRONMENT

The Indus Valley Civilisation

~4,500 years ago

History · Bronze Age · Holocene · Northgrippian

The Indus civilisation built some of the first cities, Mohenjo-daro and Harappa among them, on plains fed by the monsoon, about 4,500 years ago.

The Indus civilisation, also called Harappan after the site of Harappa, developed on alluvial plains fed by the monsoon and built some of the first urban agglomerations, including Mohenjo-daro and Harappa. Sediments and river landforms restore its trajectory: the strengthening of the monsoon sustains a dense settlement, then a regional drying, beginning about 5,000 years ago, first attenuates the floods, which probably permitted intensive plain agriculture, before continuing. The watercourses diminish or become seasonal, and from about 3,900 years before present the cities decline and are then abandoned, the populations moving eastward into more humid regions.

Why it matters

An urban complex estimated at a million inhabitants came apart without conquest, over several generations, through progressive modification of its water regime. The same climatic trend first favoured and then compromised the system, which distinguishes this case from scenarios of abrupt collapse.

Dating & uncertainty

The date retained corresponds to the urban peak, about 4,500 years ago, decline beginning around 3,900 years. The chronology rests on river landforms, lake sediments and site surveys. An older hypothesis has been set aside: no glacier-fed Himalayan river irrigated the heart of Harappan territory, only rivers of rainfall regime. The distinction is decisive, a glacier-fed river continuing to flow in the dry season through melt and cushioning a deficient monsoon, whereas a monsoon river runs dry precisely in the years when rainfall fails.

Our species’ history as one day

23:39:2520 min 34 s before midnight

if the 315,000 years of Homo sapiens were compressed into a single day