The Indus Valley Civilization was a Bronze Age civilization (3300-1300 BCE; mature period 2600-1900 BCE) extending from what today is northeast Afghanistan to Pakistan and northwest India. Along with Ancient Egypt and Mesopotamia it was one of three early civilizations of the Old World, and of the three the most widespread.

At its peak, the Indus Civilization may have had a population of over five million. Inhabitants of the ancient Indus river valley developed new techniques in handicraft (carnelian products, seal carving) and metallurgy (copper, bronze, lead, and tin). The Indus cities are noted for their urban planning, baked brick houses, elaborate drainage systems, water supply systems, and clusters of large non-residential buildings

By 1900 BC many Indus cities had been abandoned. Historians believe things started to fall apart around 1700 BC. But how did this apparently peaceful, well-organised civilisation collapse in just 200 years?

Looking at the ruins we can see many changes. The cities became overcrowded, with houses built on top of houses. Important buildings like the Great Bath at Mohenjo-Daro were built over.

People stopped maintaining the drains and they became blocked. Some traders even hid their valuables under the floors of their homes. What were they scared of? Why did this happen?

Disruptions in Trade

Trade was very important for the Indus civilisation. Their main trade partner was Mesopotamia, which was an advanced civilisation in the Middle East.

Around the time the Indus cities started to fail, Mesopotamia was going through huge political problems. Their trade networks collapsed and this would have had a big impact on the Indus cities. There would have been less work for traders and for manufacturers, who made the things which the traders sold abroad.

Some historians think this is why the cities collapsed.

We know that only the cities fell into ruins. Farmers in the Indus Valley went on living in their villages and working on their farms, but the civilisation would never return to greatness again.

The Aryan Invasion Theory

The Indus Valley Civilization may have met its demise due to invasion. In the 1940s, archaeologist Mortimer Wheeler discovered 39 human skeletons at Mohenjo-Daro. He believed that they were people killed by invaders.

The theory suggested that by using horses and more advanced weapons against the peaceful Harappan people, the Aryans may have easily defeated them.

Yet shortly after Wheeler proposed his theory, other scholars dismissed it by explaining that the skeletons were not victims of invasion massacres, but rather the remains of hasty burials. Wheeler himself eventually admitted that the theory could not be proven.

There is no evidence of war or mass killings. Indus Valley people seem to have been peaceful. Very few weapons have been found. Unlike ancient Rome and Greece, no evidence of an army has been discovered. The Indus people had few, if any, enemies and it seems that they preferred to live in peace.

Various elements of the Indus Civilization are found in later cultures, suggesting the civilization did not disappear suddenly due to an invasion.

The Climate Change Theory

Other scholarship suggests the collapse of Harappan society resulted from climate change. Some experts believe the drying of the Ghagger Hakra, which began around 1900 BCE, was the main cause for climate change, while others conclude that a great flood struck the area.

The main cities were closely linked to the river, so changes in the river flow would have had a terrible effect on Harappan society, such as crop failures, starvation, and disease. Skeletal evidence suggests many people died from malaria, which is most often spread by mosquitoes. This also would have caused a breakdown in the economy and civic order within the urban areas.

Another disastrous change in the Harappan climate might have been eastward-moving monsoons, or winds that bring heavy rains. Monsoons can be both helpful and detrimental to a climate, depending on whether they support or destroy vegetation and agriculture. The monsoons that came to the Indus River Valley aided the growth of agricultural surpluses, which supported the development of cities, such as Harappa. The population came to rely on seasonal monsoons rather than irrigation, and as the monsoons shifted eastward, the water supply would have dried up.

It is believed that at the same time, the Ghagger Hakra River (another river in the area) dried up. People were forced to abandon many of the cities located along its banks, such as Kalibangan and Banawali.

The Harappans may have migrated toward the Ganges basin in the east, where they established villages and isolated farms.

These small communities could not produce the same agricultural surpluses to support large cities. With the reduced production of goods, there was a decline in trade with Egypt and Mesopotamia. By around 1700 BCE, most of the Indus Valley Civilization cities had been abandoned.

Why do you think the Indus cities collapsed?

How did we discover the Indus Valley?

The Indus Valley lay forgotten and undiscovered for thousands of years.

In 1826, a British traveller in India called Charles Masson came across some mysterious brick mounds. He thought they looked like old castles, but didn’t know who built them.

Thirty years later, in 1856, engineers building a railway found more bricks. They carted them off and continued to build the railway. These bricks were the first evidence of the lost Indus city of Harappa.

In the 1920s, archaeologists began to excavate the sites of Harappa and Mohenjo-Daro. They had uncovered the remains of two long-forgotten cities and found the Indus Valley civilisation.

The Indus Valley people did not leave great structures, like the Pyramids of Egypt or the Great Wall of China, but they did help shape the modern world.