More than 4,000 years ago, on the banks of the Indus River in what is now Pakistan, one of humanity's greatest urban experiments was quietly defying a rule we have come to take for granted: that as cities grow rich, inequality grows with them.
New research published this week in Science Advances has found that as Mohenjo-daro flourished at the height of the Indus Valley Civilization — between roughly 2600 and 1900 BCE — the gap between its wealthiest and poorest households actually shrank. It is a finding that upends long-held assumptions about economic inequality and raises a profound question: what were they doing right?
A city unlike any other
Mohenjo-daro was, by any measure, extraordinary. At its peak it housed up to 40,000 residents in a carefully planned grid of streets, complete with sophisticated drainage systems, large public baths, communal granaries, and standardized brickwork. It had no known palaces, no royal tombs, and no obvious warrior class. It traded extensively across South Asia and into Mesopotamia. Its residents were literate, using a script that, frustratingly, still has not been fully deciphered.
The new study, led by researchers from Binghamton University and the University of Cologne, analyzed house sizes and artifact distributions at Mohenjo-daro over multiple centuries. House sizes are a well-established proxy for household wealth in archaeology — larger homes typically indicate greater affluence.
Their analysis found something remarkable: in the earlier periods of Mohenjo-daro's history, the city showed more variation in house sizes. As the city matured and grew more prosperous, that variation actually decreased. The richest households did not get dramatically richer while the poor fell further behind. The city appeared to share its wealth more broadly as it developed.
Shared infrastructure, shared prosperity
What might explain this? The researchers point to several distinctive features of Mohenjo-daro's organization. Unlike contemporary civilizations in Mesopotamia or Egypt, the Indus Valley cities appear to have lacked powerful royal elites who could concentrate wealth and resources. There was no Pharaoh, no warrior king, and apparently no standing army.
Instead, prosperity seems to have flowed through shared public infrastructure — the famous Great Bath, the communal granaries, the drainage networks — that benefited all residents regardless of status. Trade goods appear to have been distributed relatively evenly across the population. There is little evidence of the tribute extraction or hoarding of resources that characterized many other ancient societies.
"What we're seeing is a city that figured out that broad access to shared resources is good for everyone," said lead author Dr. Michael Harrower. "The wealth gap shrank not because the rich got poorer, but because the systems of the city lifted everyone."
A 4,000-year-old lesson
The findings arrive at a moment when modern cities are grappling with rising inequality of their own. Researchers are careful not to oversimplify — we still know relatively little about Mohenjo-daro's political and social structures, and the mystery of its writing system means many answers remain locked away.
But the evidence suggests something important: rising inequality is not an inevitable feature of urban prosperity. Cities have, before, been designed in ways that distribute wealth more broadly. The Indus Valley Civilization built something that worked not just for the elite, but for a diverse, complex urban population — and it lasted for centuries.
Mohenjo-daro was eventually abandoned around 1900 BCE, likely due to a combination of climate shifts and changes to the Indus river system. But the city's legacy, now illuminated by new data, offers something worth knowing: prosperity and equality are not opposites. They may, in fact, reinforce each other.
