SOCIETY × ENVIRONMENT

The Indus Cities Fade

~4,500 years ago

History · Bronze Age · Holocene · Northgrippian

The Indus civilisation raised some of the earliest cities, Mohenjo-daro and Harappa among them, on floodplains fed by the monsoon. Sediments and landforms tell the arc: a strengthening monsoon supported dense settlement, while a regional drying after about 5,000 years ago first calmed the floods, probably opening the plains to intensive farming, and then did not stop. Rivers shrank or turned seasonal, and from about 3,900 years ago the cities dwindled and emptied as people moved east toward moister lands.

Why it matters

An urban world of a million people unwound without a conquest, over generations, as its water budget failed. Here the drying works as a slow adversary rather than a catastrophe: the same trend that calmed catastrophic floods, and so probably opened the plains to intensive farming, ended by starving the rivers. Civilisations are hydraulic bets, and the climate can change the odds.

Dating & uncertainty

The anchor marks the urban peak around 4,500 years ago; decline sets in from about 3,900 years ago. The dating rests on river landforms, lake sediments and settlement surveys read together, and one long-standing idea fell to it: no glacier-fed Himalayan river watered the Harappan heartland, only monsoon-fed rivers, which is what made the system mortal.

Sources

1. Giosan et al. (2012), PNAS · Fluvial landscapes of the Harappan civilizationdoi:10.1073/pnas.1112743109
2. Dixit et al. (2018), Scientific Reports · Intensified summer monsoon and the urbanization of Indus Civilization in northwest Indiadoi:10.1038/s41598-018-22504-5
3. Dutt et al. (2019), Quaternary International · Climate variability and evolution of the Indus civilizationdoi:10.1016/j.quaint.2018.11.012

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