Introduction

In the late 1800s, archaeologists rediscovered an important ancient human society. These people lived in the Indus River Valley. It’s contained in parts of what we now know as the Middle Eastern countries India and Pakistan. Many artifacts have been found, telling us about people who lived here. Still, their writing remains a mystery. So, we are left to predict based on evidence that we do have. It comes from archaeological digs, the study of human history, and art. More recently, we’ve studied genes and DNA. These are the body’s instructions on how to grow and function, passed from parent to child.

We do know that the major cities of this society were well organized. They had advanced technology. These agricultural communities shared 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.

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

The two largest cities found from the Indus River Valley society are Harappa and Mohenjo-daro. Both are located in modern-day Pakistan. The cities are about 400 miles apart but have interesting similarities. Some parts are built on mounds, which protected them from flooding. Their high position also could likely help defend from attackers. The streets were laid out in a grid with elaborate well systems to deliver fresh water to people. A special drainage system could dump sewage outside of the city. 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. Producing and trading goods seemed to be their main focus. Trade networks were broad. Goods traveled back and forth from the Indus cities to places further out, such as Mesopotamia.

About 40,000 to 60,000 people lived in each city. With numbers that high, farming was essential to feed everyone. These cities encompassed an area much larger than the modern city-states of Mesopotamia and the society that had formed in Egypt.

Both cities began as small farming communities. They also produced handmade items such as beads and metal work. The 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 more homes. They put in roads that allowed wheeled carts to move through the city for trade. Some expanded to two-lane roads that could allow 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 involve trade. Thousands of stamp seals¹ have been found. They had a variety of animals and decorations on them. The writing on these seals has yet to be translated. Still some images show up more than others. About two of every three seals found show a unicorn. Other seals with real animals have also been uncovered. Archaeologists believe that the animal symbols 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 for the female figure shown below at right. She is shown strangling two tigers. Archaeologists, however, haven’t found any evidence of a central temple for the worship of gods. Perhaps religious beliefs were more personal for these communities. The symbols and images appear similar to those of other nearby societies. 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 could show that ideas 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. In addition, small tablets with the Indus writing and symbols have been found. Language scholars believe that these could be a numbering system. Interestingly, many of the tablets were broken in half. They may have been business contracts: each party received half of the tablet as proof of the deal. It’s like a receipt on a rock.

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 population. Still, historians still don’t know why these changes occurred, or don’t agree why.

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 repair 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, moving into the Indian subcontinent. It’s the land around what we now call India. These groups 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 people left some cities because of climate change, shifting tectonic plates, and a change in the course of rivers. Tectonic plates are large interlocking slabs on Earth’s hard outer layer, called the crust. The plates fit together like puzzle pieces far beneath our feet.

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. They 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 are often debated. Additional data is most certainly needed before making conclusions about these ancient migrations.