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World History Volume 1, to 1500

3.4 The Indus Valley Civilization

World History Volume 1, to 15003.4 The Indus Valley Civilization

Table of contents
  1. Preface
  2. Early Human Societies
    1. 1 Understanding the Past
      1. Introduction
      2. 1.1 Developing a Global Perspective
      3. 1.2 Primary Sources
      4. 1.3 Causation and Interpretation in History
      5. Key Terms
      6. Section Summary
      7. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
    2. 2 Early Humans
      1. Introduction
      2. 2.1 Early Human Evolution and Migration
      3. 2.2 People in the Paleolithic Age
      4. 2.3 The Neolithic Revolution
      5. Key Terms
      6. Section Summary
      7. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
    3. 3 Early Civilizations and Urban Societies
      1. Introduction
      2. 3.1 Early Civilizations
      3. 3.2 Ancient Mesopotamia
      4. 3.3 Ancient Egypt
      5. 3.4 The Indus Valley Civilization
      6. Key Terms
      7. Section Summary
      8. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
    4. 4 The Near East
      1. Introduction
      2. 4.1 From Old Babylon to the Medes
      3. 4.2 Egypt’s New Kingdom
      4. 4.3 The Persian Empire
      5. 4.4 The Hebrews
      6. Key Terms
      7. Section Summary
      8. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
    5. 5 Asia in Ancient Times
      1. Introduction
      2. 5.1 Ancient China
      3. 5.2 The Steppes
      4. 5.3 Korea, Japan, and Southeast Asia
      5. 5.4 Vedic India to the Fall of the Maurya Empire
      6. Key Terms
      7. Section Summary
      8. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
  3. States and Empires, 1000 BCE–500 CE
    1. 6 Mediterranean Peoples
      1. Introduction
      2. 6.1 Early Mediterranean Peoples
      3. 6.2 Ancient Greece
      4. 6.3 The Hellenistic Era
      5. 6.4 The Roman Republic
      6. 6.5 The Age of Augustus
      7. Key Terms
      8. Section Summary
      9. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
    2. 7 Experiencing the Roman Empire
      1. Introduction
      2. 7.1 The Daily Life of a Roman Family
      3. 7.2 Slavery in the Roman Empire
      4. 7.3 The Roman Economy: Trade, Taxes, and Conquest
      5. 7.4 Religion in the Roman Empire
      6. 7.5 The Regions of Rome
      7. Key Terms
      8. Section Summary
      9. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
    3. 8 The Americas in Ancient Times
      1. Introduction
      2. 8.1 Populating and Settling the Americas
      3. 8.2 Early Cultures and Civilizations in the Americas
      4. 8.3 The Age of Empires in the Americas
      5. Key Terms
      6. Section Summary
      7. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
    4. 9 Africa in Ancient Times
      1. Introduction
      2. 9.1 Africa’s Geography and Climate
      3. 9.2 The Emergence of Farming and the Bantu Migrations
      4. 9.3 The Kingdom of Kush
      5. 9.4 North Africa’s Mediterranean and Trans-Saharan Connections
      6. Key Terms
      7. Section Summary
      8. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
  4. An Age of Religion, 500–1200 CE
    1. 10 Empires of Faith
      1. Introduction
      2. 10.1 The Eastward Shift
      3. 10.2 The Byzantine Empire and Persia
      4. 10.3 The Kingdoms of Aksum and Himyar
      5. 10.4 The Margins of Empire
      6. Key Terms
      7. Section Summary
      8. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
    2. 11 The Rise of Islam and the Caliphates
      1. Introduction
      2. 11.1 The Rise and Message of Islam
      3. 11.2 The Arab-Islamic Conquests and the First Islamic States
      4. 11.3 Islamization and Religious Rule under Islam
      5. Key Terms
      6. Section Summary
      7. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
    3. 12 India, the Indian Ocean Basin, and East Asia
      1. Introduction
      2. 12.1 The Indian Ocean World in the Early Middle Ages
      3. 12.2 East-West Interactions in the Early Middle Ages
      4. 12.3 Border States: Sogdiana, Korea, and Japan
      5. Key Terms
      6. Section Summary
      7. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
    4. 13 The Post-Roman West and the Crusading Movement
      1. Introduction
      2. 13.1 The Post-Roman West in the Early Middle Ages
      3. 13.2 The Seljuk Migration and the Call from the East
      4. 13.3 Patriarch and Papacy: The Church and the Call to Crusade
      5. 13.4 The Crusading Movement
      6. Key Terms
      7. Section Summary
      8. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
  5. A Global Middle Ages, 1200–1500 CE
    1. 14 Pax Mongolica: The Steppe Empire of the Mongols
      1. Introduction
      2. 14.1 Song China and the Steppe Peoples
      3. 14.2 Chinggis Khan and the Early Mongol Empire
      4. 14.3 The Mongol Empire Fragments
      5. 14.4 Christianity and Islam outside Central Asia
      6. Key Terms
      7. Section Summary
      8. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
    2. 15 States and Societies in Sub-Saharan Africa
      1. Introduction
      2. 15.1 Culture and Society in Medieval Africa
      3. 15.2 Medieval Sub-Saharan Africa
      4. 15.3 The People of the Sahel
      5. Key Terms
      6. Section Summary
      7. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
    3. 16 Climate Change and Plague in the Fourteenth Century
      1. Introduction
      2. 16.1 Asia, North Africa, and Europe in the Early Fourteenth Century
      3. 16.2 Famine, Climate Change, and Migration
      4. 16.3 The Black Death from East to West
      5. 16.4 The Long-Term Effects of Global Transformation
      6. Key Terms
      7. Section Summary
      8. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
    4. 17 The Ottomans, the Mamluks, and the Ming
      1. Introduction
      2. 17.1 The Ottomans and the Mongols
      3. 17.2 From the Mamluks to Ming China
      4. 17.3 Gunpowder and Nomads in a Transitional Age
      5. Key Terms
      6. Section Summary
      7. Assessments
        1. Review Questions
        2. Check Your Understanding Questions
        3. Application and Reflection Questions
  6. A | Glossary
  7. B | World History, Volume 1, to 1500: Maps and Timelines
  8. C | World Maps
  9. D | Recommended Resources for the Study of World History
  10. Index

Learning Objectives

By the end of this section, you will be able to:

  • Analyze the growth, development, and decline of the Indus valley culture
  • Describe the cities of Mohenjo-Daro and Harappa
  • Identify key themes in Indus valley religion and culture

More than fifteen hundred miles east of Mesopotamia, in the fertile valley of the Indus River, another early civilization developed in the early third millennium BCE as a peer of ancient Sumer. Early in the second millennium BCE, however, the cities of this Indus valley culture experienced decline. Lacking written records, historians have only cultural artifacts on which to base any speculation about the rise and fall of this spectacular culture, which undoubtedly influenced subsequent civilizations that arose in South Asia.

The Origins of the Indus Valley Civilization

The Indus River flows from the Himalayan Mountains south into the Indian Ocean, depositing rich alluvial soil from the mountains along its banks. Its valley (in modern Pakistan and India) thus provided a hospitable environment for population growth for the emerging Indus valley civilization (c. 2800 BCE–1800 BCE).

Evidence for the domestication of plants and animals in this region dates to about 7000 BCE, but the process may have begun earlier. It is likely that agriculturalists in the region adopted barley and wheat cultivation techniques from the Near East, where people had been practicing agriculture for thousands of years by this point. However, it is also possible that the people of the Indus valley developed some of these techniques independently. Regardless, by about 5000 BCE, they were clearly in contact with the civilizations in Egypt and Sumer.

The farmers of the Indus valley cultivated wheat and barley as well as raised cattle and sheep, as did the farmers of Mesopotamia and western Asia. They also domesticated and cultivated bananas and cotton for cloth production, which were both unknown in ancient Mesopotamia. Thanks to the Neolithic Revolution, which secured a stable food source and stimulated population growth, people began living in settled communities along the Indus River valley as a new early civilization developed.

Beginning around 2800 BCE, the Indus valley entered a new phase in its development with the growth of a great number of urban centers. The two largest cities emerged at what are now the archaeological sites of Harappa in the northeast and Mohenjo-Daro to the southeast and downriver. Other large urban centers existed at Dholavira, Ganeriwala, and Rakhigarhi, along with many smaller but similarly organized cities scattered across the valley. By the time this civilization reached its height around 2000 BCE, more than one thousand urban centers of varying sizes were spread across the expansive region (Figure 3.24).

A map is shown with land in beige and water in blue. The Arabian Sea is labelled in the southwest and the Bay of Bengal is labelled in the southeast.  A “C” shaped area off the northeastern coast of the Arabian Sea is highlighted orange and the Indus River runs through the middle, from northeast to southwest. Areas labelled with red dots, from north to south, in this orange area are: Harappa, Ganweriwala, Rakhigarhi, Mohenjo-Daro, and Dholavira. Cities labelled with black dots in this orange area are, from north to south: Manda, Rehman Dheri, Nausharo, Ropar, Banawali, Kalibangan, Mitathal, Sutkagen-Dor, Sotka Koh, Ghazi Shah, Kot Diji, Balakot, Chanhu-Daro, Amri, Allahdino, Surkotada, Kuntasi, and Lothal. A small oval area in the far north is also highlighted orange with the city of Shortugai labelled with a black dot within.
Figure 3.24 The Indus Valley Culture. The Indus valley civilization was spread over a very large area that today includes parts of Pakistan and India. By 2000 BCE it was highly urbanized, with several large cities and as many as a thousand smaller urban areas. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Despite the large size of this civilization, its existence was unknown to modern scholars until the early nineteenth century when British excavations revealed the ancient city of Harappa. Because Harappa was the first major site discovered by archaeologists, the term Harappan often appears as a synonym for Indus valley civilization.

The archaeological sites of Harappa in the north and Mohenjo-Daro in the south have received the most study of all the Indus valley cities and remain the best known. At their height, they likely had populations of about thirty thousand people each. The political organization across the Indus valley remains imperfectly understood, but it may have consisted of a collection of independent city-states, such as existed in ancient Sumer. It is equally plausible, however, that the few large cities functioned as regional capitals ruling over the surrounding smaller ones. The fact that the sites all possessed a similar structural organization, with a sophisticated grid of well-laid-out city streets, lends credibility to theories that some form of central authority was operating.

All the cities are divided into two sections: a lower city that was largely a residential area, and an upper city or citadel that was walled off from the rest of the settlement (Figure 3.25). This citadel may have served as a monumental ceremonial center for ritual activities and the residence of the ruling elite, like the palaces and temples of Egypt and Mesopotamia. At Harappa, the wall of mud-brick enclosing the citadel was forty-two feet thick at its base and nearly fifty feet high (about as tall as a five-story building today), with rectangular towers at regular intervals. Within the citadels stood platforms built of mud-brick where ritual activities such as animal sacrifices may have been performed; at Harappa, the platform was twenty-three feet high. At the site of Kalibangan, in northwestern India, archaeologists uncovered a pit on top of the platform containing burned cattle bones.

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Figure 3.25 The Citadel Mound at Mohenjo-Daro. The stupa at Mohenjo-Daro, located in present-day Pakistan, was built circa 2500 BCE. The identification and dating of the stupa in 1923 by Indian archaeologist Rakhal Das Banerji led to the first major excavations at the site in the 1920s and 1930s. (credit: "Stupa at Mohenjo-Daro" by Omair Anwer/Flickr, CC BY 2.0)]

The citadels also included public baths. At Mohenjo-Daro, the tank of the bath was forty feet long and twenty-three feet wide and entered by staircases on either side. A nearby well provided the water. Archaeologists have uncovered a large hall supported by pilasters composed of mud-brick at Mohenjo-Daro, as well as a multistory residence built around an open courtyard. This evidence suggests that ritual specialists, perhaps priests, lived and performed religious functions in the citadels that may have required them to bathe in the large public bath and congregate in the hall. An extensive granary for grain storage was found at Mohenjo-Daro. Farmers from outlying rural areas undoubtedly produced the surplus crops that were stored here to provide sustenance for the elite, religious specialists, and other city residents such as merchants and artisans, just as in Mesopotamia and Egypt.

The lower sections of the Indus valley cities consisted of residential quarters and workshops. At Mohenjo-Daro and Kalibangan, the houses typically consisted of four to six rooms built around a central courtyard and were equipped with wells to provide running water to a bathroom. Larger homes in the cities were multistory with as many as thirty rooms. There is also evidence of devices attached to some of the roofs that pumped wind into homes and other large buildings to cool them.

The Indus valley cities also included an industrial area where workshops were located. At Harappa, this district included quarters for the laborers who worked there. The ancient city at the site of Lothal near the Indian Ocean included a dockyard and a warehouse for incoming trade goods. The inhabitants of these cities may have included the artisans and merchants who provided goods for the ruling elite. As in ancient Mesopotamia and Egypt, the majority of the population were probably farmers who lived in the outlying rural areas surrounding each city.

Trade, Writing, and Religion

Archaeological work has revealed that a considerable amount of trade flowed between Mesopotamia and the Indus valley. Cuneiform tablets from Mesopotamia refer to the Indus valley as Meluhha and document that precious stones such as lapis lazuli and carnelian, as well as marine shells from the Indian Ocean, were imported from there. Merchants traveled by sea across the Indian Ocean and by land over the Iranian plateau (Figure 3.26).

A map with three sections of land. In the southwest, Egypt and Nubia are labelled with the cities of Memphis and Thebes located on blue waterways. In the northwest, Crete is labelled with the city of Troy labelled to the north and Tyre labelled to the east. In the middle of the map, the Hittite Empire is labelled and highlighted in a green oval. To the southeast, the Mitanni State is highlighted in a rough square of orange. Heading southeast, Assyria is labelled and highlighted in a green oval. The cities of Ninevah and Assur are labelled within. To the south, Babylonia is labelled and highlighted in a purple oval. The cities of Babylon, Susa, and Ur are located within. A label for Sumer is located in the south of this purple area.  In the far east of the map, Indus is labelled. A red line with arrows at both ends runs from Babylonia to Indus and back. A purple double arrowed dashed line runs in the water from Indus to the city of Ur and back.
Figure 3.26 Indus Valley Trade with Mesopotamia. From the work of archaeologists, we know that significant trade took place between the inhabitants of the Indus River valley and their contemporaries in Mesopotamia. (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

The influence of Mesopotamia on the Indus valley culture is evident in the use of seals. The Indus valley seals were inscribed with depictions of human figures and animals such as bulls and goats, likely totems for families or lineages, and brief inscriptions that likely indicate names, titles, or occupations. Merchants marked ownership of goods by making an impression of the seal on the soft clay that covered the mouth of the jar or other vessel that held the objects, or on clay tags attached to sacks of grain (Figure 3.27). A similar practice occurred in contemporary Mesopotamia, where the seal was in the shape of a cylinder that could be rolled to leave an impression. Archaeologists have found seals from the Indus valley in ancient Sumerian cities such as Ur.

A picture of two square objects is shown on a grayish-blue background. The one on the left is white and smaller, while the one of the right is a bit bigger and a cream color. The images on the square on the right are raised from the back. They show a horse-type creature with ornamental reins around its neck and a long, pointy horn extending out its head. Above the animal are four shapes – a diamond with a v-shape inside, a triangle with lines inside, and a line, while the fourth shape is indistinguishable. Below the head of the animal is a long stick with a square at the top and a half-circle below. Both shapes have lines on them. The square at the left is an impression of the first square, showing everything backward and inside the stone as opposed to sticking out as in the other square.
Figure 3.27 An Indus Valley Seal. On the left is a seal from the Indus valley civilization, and on the right is a modern clay impression made from it. Such seals typically showed animals and a script that remains to be deciphered. (credit: modification of work "Stamp seal and modern impression: unicorn and incense burner (?)" by Dodge Fund, 1949/The Metropolitan Museum of Art, Public Domain)

The script that appears on many of the seals is unique to the people of the Indus valley civilization, and scholars have yet to decipher it. It seems to consist of phonograms, signs for the sounds of syllables, and there appear to be about four hundred such signs. Many speculate that the language written in this script may be related to the Dravidian languages still spoken across southern India today. It may also be similar to the script invented by the Elamites of southwestern Iran. Unlike the case in Mesopotamia and Egypt, archaeologists have not uncovered clay tablets or papyrus rolls in the Indus valley.

The Past Meets the Present

Deciphering Indus Valley Script

One of the great mysteries surrounding Indus valley script is what exactly it represents. Was it a means of capturing spoken language, or did the marks simply indicate whether taxes had been paid on an item or signify the quality of a particular good (in the same way we use stars to rate products and services online today)?

Rajesh Rao, a professor of computer science at the University of Washington who became fascinated with the Indus valley civilization as a child in India, created a computer program to help him answer this question by measuring conditional entropy in Indus valley writing. Conditional entropy measures the degree of randomness in a sequence. In a system of writing that encodes language, there is a fairly low level of randomness. Letters appear frequently in some combinations and rarely or never in others. For example, in the English language, the letter q is usually followed by the letter u and never by the letter k. At the beginning of a word, the letter h is never followed by a consonant.

Rao tested the conditional entropy of the Indus valley script along with that of several natural languages including English, artificial languages such as those written for computers, and other sequences not related to language such as human DNA sequences. He discovered that the Indus valley script has a degree of randomness similar to that of natural languages, leading him to the conclusion that the symbols do represent a language and are not simply marks of quality or signs that something has been taxed. He also concluded that the rate of conditional entropy in Indus valley writing resembled that of Old Tamil, an earlier form of the Tamil language currently spoken in southern India that belongs to the Dravidian language family. This idea angered many Indians, especially those who speak Hindi, a language derived from Sanskrit that is the first language of many people in northern India. This issue is both historical and modern. If the language of the ancient Indus valley was Dravidian in origin, it calls into question the ancestry of the people who lived there, and given the evolution of the caste system, it raises questions about social identities that have existed for centuries. The issue remains in question, and the controversy about ancestral origins is far more complex than the single issue of language.

  • Why do you think the origin of language matters so much to the people of India?
  • If Indus valley writing were deciphered, what could historians learn about the culture that we cannot currently know?
  • In what other ways could computers help historians learn about the past?

Bronze technology probably also entered the Indus River valley by the third millennium BCE through trade with Mesopotamia. Merchants from the Indus valley may even have exported tin from Afghanistan to Mesopotamia, since this metal was in demand for the manufacture of bronze.

Notwithstanding the many obvious Mesopotamian influences and trading connections, the people of the Indus valley civilization developed their own unique culture. Their distinctive religion may have shaped later cultures in India. For example, clay figurines from the Indus valley that are believed to depict deities are often interpreted as portraying a goddess whose female attributes are similar to those of the Hindu goddess Durga, consort of the god Shiva. Some seals depict a horned three-faced figure surrounded by animals, which closely resembles the Hindu deity Shiva when represented as the Lord of the Animals (Figure 3.28). Archaeologists have also found stones molded into shapes that resemble lingams and yonis, which are representations of male and female sexual organs associated with the worship of Shiva. The people of the Indus valley buried their dead with modest grave goods such as clay pots, which suggests a belief in an afterlife. However, there is no evidence of temples or monumental tombs such as the Egyptian pyramids or the royal tombs of Ur in Mesopotamia.

Two pictures are shown on a dark black background. (a) The first picture shows a caramel-colored stone carving with a large piece missing from the bottom right. The middle of the stone shows a man facing forward with a rectangular face, large nose, and almond shaped eyes. A face is also shown on either side of his head. He wears a large hat with round horns on both sides. He wears clothing with stripes all over and is sitting on a footed platform. There is a goat-type creature under the platform with two horns. Various animals can be seen around his head (two horned animals on the left, snake and fish type animals above his head and an elephant and tiger type animals on the right). A small carving of a person is seen to the far right. (b) This stone carving is colored off white and shows a person’s head and chest. They have full lips, closed eyes, and a highly etched tall headdress on their head. There is another head on either side of their head that appears similar. Rows of necklaces hang from their neck and there are some carvings seen on the bottom right of their chest. The background shows darker colored stone and black above the head.
Figure 3.28 Possible Influence of Indus Valley Religious Imagery. Historians speculate that the religion of the Indus valley might have influenced later Indian cultures. For example, a seal from 2600–1900 BCE discovered at Mohenjo-Daro (a) shows a seated figure with three faces surrounded by animals. A much later sixth-century CE portrayal of Shiva from the Elephanta Caves in western India (b) shows the Hindu god seated, also with three faces and surrounded by animals. (credit a: modification of work "Shiva Pashupati" by Unknown/Wikimedia Commons, Public Domain; credit b: modification of work "Elephanta Caves" by Christian Haugen/Flickr, CC BY 2.0)

The artisans of the Indus valley created unique sculptures in clay, stone, and bronze. One of the more spectacular stone works from Mohenjo-Daro depicts a serene bearded man who may be a priest or leader in the community. A tiny bronze figure appears to represent a young woman dancing (Figure 3.29). Her bracelets and necklaces indicate that the people of this culture employed artisans to manufacture such adornment, which may have indicated high social status. Artisans of the Indus valley were also very busy manufacturing pottery and seals. Their artistic designs influenced artisans in neighboring cultures over a wide area, from the upper Ganges River valley in what is today northwestern India to Baluchistan in western Pakistan and southeastern Iran.

A picture of a black statue of a lady on an off-white platform is seen. Her shadow reflects behind her on a white background. The statue has long hair in a low ponytail with closed eyes and a half-smile on her face. She wears a necklace with three oval objects hanging in front. Her right hand rests on her hip and her left arm hangs down with her fist resting above her bent left knee. Bangles adorn both her arms. Her feet are missing and her right leg is anchored to the platform below while the left leg is resting in the air.
Figure 3.29 The Mohenjo-Daro Dancer. This four-inch-tall bronze statue of a young woman discovered at Mohenjo-Daro and dated to circa 2300–1750 BCE could depict a goddess or a woman of the elite class who is dancing. If she is dancing, we can also conclude that music and dance may have been incorporated into social and religious rituals. (credit: modification of work "Bronze ‘Dancing Girl,’ Mohenjo-daro, c. 2500 BC" by Gary Todd/Flickr, Public Domain)

Merchants from the Indus valley were undoubtedly active in exchanging such wares in these regions. In the absence of coinage, they used a common system of stone cubical weights to assess goods in commercial exchanges that required barter. The cities of the Indus valley could have also used these weights to assess taxes in kind that they collected for their granaries.

The Era of Decline

Beginning around 1800 BCE, the centuries of trade between the Indus valley and Mesopotamia came to an end. Over the next four centuries, the cities of the Indus River valley were slowly depopulated, and the civilization declined, likely in stages. Why and how this decline occurred remains unknown. One common view is that it was related to regional climate change. Around 2000 BCE, the floodplain of the Indus River shifted dramatically, creating dry river beds where cities had been and water once flowed. Changes in the pattern of seasonal wind and rainfall, known as the monsoon in South Asia, may have caused these environmental effects. Without a secure source of water for drinking and irrigation, the cities would have suffered declines in population. Another theory suggests that centuries of environmental degradation caused by urbanization and large population growth made the land unsuitable to human populations. Still other views point to the possibility of tectonic activity that changed the course of the rivers, or even epidemic disease that decimated the population.

Before these environmental factors began to be considered, the view for many years was that the Indus valley civilization was violently destroyed in a conquest by nomadic Indo-European speakers calling themselves Aryans, a Sanskrit-speaking group of nomadic pastoralists who raised cattle and horses. Some Aryans began migrating from the Eurasian Steppe north of the Black and Caspian Seas around 3500 BCE. Over time, different groups spread into Europe, Anatolia, Iran, and eventually Pakistan and India.

The Aryan invasion theory of decline depends heavily on Indo-European works of religious literature like the Rigveda, produced sometime between 1500 and 1000 BCE in northwestern India. This work includes a great number of hymns, rituals, descriptions of deities, and other largely religious topics geared toward understanding the origin of the universe and the nature of the divine. But in parts it also discusses the arrival of the Aryans and describes them attacking the walled cities and forts of the indigenous population. While some of these descriptions were likely developed centuries after the fall of the Indus valley civilization and may be unrelated to it, some scholars continue to hold that these passages describe the conquest of Mohenjo-Daro. Archaeological evidence attesting to the fact that Mohenjo-Daro was attacked around 1500 BCE and mostly destroyed lends some credibility to these claims.

We may never know what best explains the collapse of the Indus valley civilization. A few or all these causes may have played a role. For example, environmental degradation caused by years of resource exploitation and high population density certainly had an effect. These issues could have been compounded by climate change and disease. And in a weakened state, the people of the region would have been far more vulnerable to attack by raiding groups like the Aryans.

However it happened, by around 1500 BCE, the social and political systems had broken down, and the sophisticated culture of the Indus valley civilization had collapsed. The architectural styles that characterized the cities at their height were abandoned, as was the writing system, the sophisticated metalworking, and other artisanal crafts. The Indus valley civilization had come to an end.

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