Introduction

Archaeologists rediscovered the ancient societies of the Indus River Valley in the late nineteenth century. They lived in parts of what we now know as the Middle Eastern countries India and Pakistan. Digs that began in the 1920s have provided many artifacts from the people who lived here. Still, their writing remains a mystery. So, we are left to make conclusions based on the evidence that we do have: archaeological, anthropological, artistic, and more recently, genetic studies. Genes contain the information for how our bodies grow and function. They get passed down from parent to child.

What we do know is that the major cities of this society were well organized and technologically advanced. These agricultural communities shared common bonds based upon religious or spiritual beliefs and language and trade networks. The society appears to have declined around 1700 BCE. Historians and archaeologists continue to debate the causes of this decline.

Harappa and Mohenjo-daro (c. 3500—1700 BCE)

The two largest cities of the Indus River Valley society that have been unearthed are Harappa and Mohenjo- daro, both located in modern-day Pakistan. The cities are about 400 miles from each other but have interesting similarities. Some parts are constructed on mounds that provided protection from flooding. They could have also been positioned that way to easily defend from attackers. The streets were laid out in a grid with elaborate well systems to deliver fresh water to people. An advanced drainage system could dump sewage outside of the city near the agricultural fields. Neither city had a central palace or temple structure. It’s possible this society was run by several wealthy families rather than a central ruler. The production and distribution of goods seemed to be their main focus. Trade networks were broad and goods traveled back and forth from the Indus areas and places further out, such as Mesopotamia.

Each city’s population has been estimated from 40,000 to 60,000. With numbers that high, farming was necessary to feed everyone. These culturally connected cities encompassed an area much larger than the modern city-states of Mesopotamia and the Egyptian society.

Both cities began as small farming communities. They also produced handmade items such as beads and metal work. These cities grew over time to become important trading areas. As their wealth grew, so did their size. More mounds were added with structures for producing goods, along with residential areas. They put in roads that allowed wheeled carts to move through the city for trade. Some expanded to two-lane roads that could accommodate even more traffic. (Yes, sadly, there was traffic back then, too.)

Writing, Trade, and Spiritual Beliefs

The most significant forms of writing that we have of these societies also have to do with trade. Thousands of stamp seals¹ have been found that have a variety of animals and decorations on them. While the script on these seals hasn’t been translated, some images show up more than others. More than 65 percent of the seals found show a unicorn. Other seals with real animals have also been uncovered. Archaeologists believe that the animal motifs represented a wealthy family or person. These would have been used to mark their goods for trading purposes. It’s possible that some of the seals had religious significance. For example, the seated male figure below that is shown with a horned headdress appears often. He may be a god, but we do not know for sure.

The same theory holds true for the female figure (shown below at right) that is strangling two tigers. Archaeologists, however, haven’t found any evidence of a central temple for the worship of gods. It may be that religious beliefs were more personal for these communities. The symbols and images appear similar to those of other nearby cultures. The image of a god-like figure strangling wild beasts such as tigers can also be found in the Mesopotamian Epic story of Gilgamesh.² This may be evidence that ideas and beliefs got shared through trade networks.

Researchers have also found pottery with some of the same markings as those on seals. Such signs could suggest another connection between the seals and wealthy families involved in trade. Furthermore, small tablets with the Indus script and symbols have been found. Language scholars believe that these could be a numbering or accounting system. Interestingly, many of the tablets were broken in half. They may have been business contracts where each party received half of the tablet as proof of the deal—a rock receipt.

Trade networks certainly peaked between 2600 and 1900 BCE. Very many items from different societies, dating to that period, have been found in the region. The beautiful blue stone called Lapis lazuli and metals such as gold, silver, and tin have all turned up in Harappa. These would have traveled from areas such as modern-day Afghanistan and Iran. Harappan pottery, seals, and weights have been found in many modern societies such as those in Mesopotamia. From about 1900 BCE, some of the main cities experienced changes in habitation and population. Still, despite more evidence discovered in recent decades, historians still don’t know why these changes occurred. Or they don’t agree on the reasons.

Decline? Invasion? Transition?

The people of Mohenjo-daro deserted the city about the same time Harappa declined, or people left the cities. According to environmental historians and geographers, the river that supplied fresh water to Mohenjo-daro changed course. That would have been a good reason to leave town. Archaeologists have noticed less maintenance of drains and roads in Harappa from about 1900 BCE. They believe that this may have been the result of resources being spread too thin. Decreased trade, overpopulation, and climate change were likely to blame.

For many years, experts wondered if Indo-Europeans invaded the Indus River Valley region. We do have evidence of a group of Indo-Europeans from the Eurasian steppes, or grasslands. They moved into the Indian subcontinent—the area around what we now call India. They brought their language, knowledge, and horses and chariots, which were pretty high-tech at the time. Modern genetic studies³ show that, rather than invading, the Indo-Europeans migrated and mixed in with the native people of the Indian subcontinent. But they likely did not cause the population to decline or shift.

Today, most scholars believe that environmental factors such as climate change, shifting tectonic plates, and a change in the course of rivers contributed to the abandonment of some cities like Mohenjo-daro and the shift in population of others like Harappa. Tectonic plates are large interlocking slabs that connect like puzzle pieces below our feet, part of the outer layer of Earth known as the crust.

The Indus River Valley communities did not die out or collapse. Populations migrated in some areas and trade declined. Still, the culture lived on and transformed for many more years.

1 Stamp seals were carvings made in stone that were then used to stamp (make impressions) in soft clay that was then hardened.
2 According to most scholars, the Epic of Gilgamesh is the oldest surviving work of literature (2100 BCE).
3 Note that these genetic studies can be controversial. Additional data is most certainly needed before making conclusions about these ancient migrations.