The Indus civilization is one of the great mysteries of the ancient world. An urban society, it was made up of hundreds of cities and towns that stretched across what are today northern India and Pakistan. Though its inhabitants left great art and elaborate water infrastructures behind, we know almost nothing about the Indus people who lived between 3,000 and 1300 BCE. In fact, we still haven't even deciphered their written language.

But now, the results of a new long-term study of the northwestern Indus region have given us a new understanding of how this civilization functioned. We've also gotten hints about how the civilization coped with dramatic climate change from ever-changing weather patterns.

An international team with the Land, Water, and Settlement project in northwest India studied Indus settlements in that region between 2007 and 2014, looking at everything from water systems and plant remains to art and pottery. What they found has overturned conventional wisdom about who the Indus people were and how they lived. Now they've published a treasure trove of new findings about local centers in the Indus civilization in Current Anthropology.

Monsoon crisis

University of Cambridge archaeologist Cameron Petrie and his team found that settlements in the Indus Valley 5,000 years ago did not represent a unified culture, though clearly they shared many things in common. Some symbols and pottery styles are found in hundreds of settlements, but many were not. And when it came to farming and water management practices, each Indus settlement seemed to have its own ways of doing things.

Crops varied widely from place, though rice and millet were staples. Even growing seasons varied, with some settlements preferring winter crops and others preferring summer. Still others seemed to prefer a mix of both. The reason for this wide variation had a lot to do with access to water. The Indus region is at an environmental crossroads where monsoon rainfall varies dramatically from place to place.

Indus cities and towns, even ones that were essentially neighbors, adapted to very different patterns of rainy and dry seasons. Some used monsoon rains to water crops, others waited for rain-swollen local rivers to flood fields, while still others built reservoirs to maintain a water supply year-round. The biggest Indus cities, Mohenjo-daro and Harappa, are famous for their sophisticated waterworks, far more advanced than those of their trade partners in the great cities of Mesopotamia. Though other civilizations of the same era left behind monumental ziggurats and pyramids, the Indus left reservoirs and fountains.

Then, at the height of Indus urbanization, when the region's cities were growing the largest they had ever been, climate disaster struck. The life-giving monsoons weakened starting in roughly 2200 BCE. Drought crept into some regions, while others were relatively unaffected. And yet the Indus settlements survived for centuries afterward. Writing in Current Anthropology, the researchers say this is why the story of the Indus region "provides a unique opportunity to understand how an ancient society coped with both diverse and varied ecologies as well as change in the fundamental and underlying environmental parameters."

Studying the Indus civilization might give us hints about what it takes for cities to make it through a period of dire climate change.

Mobility and diversity

One of the intriguing discoveries that's come out of the Land, Water, and Settlement project is that the Indus cultures seem to have been uniquely qualified to deal with a climate crisis. Even before the monsoon rains slackened, each Indus settlement was used to adapting quickly to new weather patterns. At the very least, they dealt with a season of floods and a season of drought every year. Beyond that, rainfall could also vary a lot over longer periods.

Preliminary evidence suggests that many settlements may have moved around quite a bit to follow farm-friendly wet weather. The researchers suggest that when we look at the hundreds of settlements left behind by the Indus peoples, we have to consider the possibility that only 5-10 percent of them were occupied at any given time. Maybe these countless cities are the remains of just a few groups setting up camp in new areas every generation. We have strong evidence that Indus population centers moved from west to east over a period of roughly 1,500 years, until finally people abandoned their cities entirely and returned to a rural way of life.

Indus people weren't just changing their locations all the time. They also changed what they ate. It seems that they planted new kinds of crops, depending on what the environment could support. Winter crops like rabi-wheat, barley, pea, lentil, and chickpea could be swapped out for summer crops like kharif-millet, rice, and tropical pulses. Often, Petrie and his team would find a mix of winter and summer crops, as if people were experimenting to find out what grew best and when.

The researchers write:

Such an environment may have required settled populations to be relatively mobile in order to survive a constantly shifting hydrology, and there may have been high population mobility between settlement locales. Individual families or kin groups potentially spread their members between multiple settlements, and individuals or groups might have moved between settlements to access available water in times of shortage or stress.

Panarchy

What's fascinating is that ecological diversity in the Indus valley seems to be echoed by a strong cultural diversity among the people of the Indus civilization. Anthropologists sometimes call this phenomenon "panarchy" to describe the interaction between environment and social structure.

Indus cities and villages produced their own unique farming practices as well as unique styles of art. Some of the researchers found "region-specific styles of pottery" in villages, unlike pottery found anywhere else, intermingled with "characteristically Indus material" like bangles and blue beads, which are found throughout the Indus region. This suggests strong local identities supplemented a broader Indus culture. We know that migration between villages and cities was common, so it's likely that people in the Indus valley thought of themselves as part of an overarching civilization. But evidence strongly suggests it was a multicultural society, meaning that there were a lot of cultural differences at the local level, too.

Current Anthropology

Current Anthropology

It was probably this multicultural aspect of Indus life that helped people survive climate change. Rather than depending on one kind of water management system or a few staple crops, the civilization was built around diverse and redundant practices. As the researchers put it, "Indus populations in some regions were well adapted to living in diverse and changeable ecological and environmental conditions and were thus well placed to make sustainable and resilient decisions in the face of environmental change." The more centralized and homogenous the culture, the more fragile it is when dealing with environmental shifts. Having many strategies and many cultures allowed the Indus civilization to react nimbly, adapting fast to environments that were literally transforming before their eyes.

Current Anthropology, 2017. DOI: 10.1086/690112