How did the Indus Valley Civilization collapse

In 1893, the British archaeologist Sir Alexander Cunningham discovered traces of a highly developed ancient culture in India. At the time, no one suspected that it belonged to an unknown civilization. For many years, these finds were thought to be the remains of Sumerian settlements in India. No one imagined that an ancient civilization had once existed here, one that was a contemporary of ancient Egypt, Mesopotamia, and China. Only in 1922 did another British archaeologist, John Marshall, excavate Harappa and Mohenjo-Daro and show that these were not Sumerian cities, but the remains of an entirely different civilization whose existence humanity had never suspected. Cities with straight streets, sewer systems, public baths, and long-distance trade. All of these existed 4,000 years ago, but there is one problem. We still can't read a single one of their texts. We do not know the names of their kings, we do not know their gods, and we don't even know what they called themselves. And yet this civilization was the largest in the ancient world, so who were the people that created it? Around 7,000 years ago, the Indus Valley, in what is now Pakistan and India, the hunter-gatherers who lived there gradually began to adopt agriculture, and the first permanent settlements started to appear. The most famous of them is Mehrgarh. These were not yet cities, but small villages where people began farming the land instead of relying on gathering wild plants and hunting animals. They cultivated wheat, barley, and millet, and later started raising livestock. Here the foundations were laid for what would eventually become one of the greatest civilizations of the Bronze Age. It's hardly surprising that this process began here. The region offered extremely favorable conditions for settled agriculture. Today, northern India and Pakistan are largely semi-desert, but at the time, the landscape was covered with tropical forests, nourished by seasonal monsoon rains. The Indus and Saraswati rivers regularly flooded, depositing rich layers of silt and making the surrounding soil exceptionally fertile. But who were the people that lived here? We do not know for certain. Many scholars believe that the population of the Indus Valley civilization was proto-Dravidian. This hypothesis has strong supporting evidence, but it cannot yet be proven conclusively. The Harappan script remains undeciphered, and genetic studies have not produced a definitive answer. When researchers analyzed human remains found in Harappan cities, they identified Dravidian genetic markers. And at the same time, some samples contain other genetic components, suggesting that the population may have been mixed. This period is known as the Pre-Harappan period. People lived in small villages or in small farming communities that cultivated the land. Yet there was little rapid development. For more than a thousand years, their way of life changed very little. Their reasons were simple. People lived in favorable climatic conditions, had plenty of food, and faced no serious external threats. In such circumstances, there was little reason to change anything radically. Over time, however, the climate in the northern hemisphere began to grow cooler and increasingly dry as the tilt of the Earth's axis gradually changed. The monsoon winds shifted southward, and regions along the Tropic of Cancer began to undergo aridization, the same process that later produced the Sahara and Arabian deserts. Similar changes were taking place in the region where the Indus Valley civilization would eventually emerge. The climate became progressively drier, forests retreated, and growing food became more difficult. Paradoxically, this deterioration of conditions pushed development forward. People were forced to cooperate more closely in order to cultivate the land. Clans united into tribes, tribes formed larger confederations, and eventually this process led to the emergence of a civilization. Between 2800 and 2300 BC, during what is known as the Early Harappan Period, large settlements began to appear across the region. Many of them would later develop into true cities. Trade expanded, new crafts emerged, and the political organization of society appears to have grown more complex. The first real cities began to take shape. The cities of the Indus Valley civilization are remarkable. They were built according to a unified plan. Wide streets and avenues divided the cities into clearly defined blocks. This is one of the earliest known examples of planned urban design, with cities laid out in a grid of rectangular blocks. Even within these blocks, houses followed similar layouts. What is especially striking is that archaeologists find very little evidence of strong social inequality. There doesn't appear to have been extremely wealthy elites or very poor groups. Most residents seem to have lived at roughly the same level. This becomes particularly clear when compared with other civilizations. For example, when archaeologists excavate Roman cities such as Pompeii, they uncover small houses of poor alongside luxurious villas owned by wealthy Romans. Large public buildings stand nearby, temples, bath complexes, and other monumental structures. In the cities of the Indus Valley civilization, nothing like this appears. Most houses look very similar to one another. They're not identical, but they're roughly the same size. Some are slightly larger, others are slightly smaller, yet there's no striking contrast between them. Residential buildings were usually two or three stories tall and often formed a square around an inner courtyard. The entrance to a house almost never opened directly onto the main street. Instead, doors typically led into narrow side alleys. But the real revolution was not the architecture of the houses themselves, but what lie inside and beneath them. The cities of the Harappan civilization had one of the earliest sewer systems in the world and, without exaggeration, the most advanced in the ancient world. The level of sophistication was extraordinary. For example, Paris only built a sewer system of comparable complexity in the 19th century, and some cities in South Asia still lack one today. Beneath this street stretched a complex network of drains and sewage channels. Almost every house was connected to it. Many homes had toilets with flushing systems and separate rooms for washing. Water flowed through vertical clay pipes built into the walls or along open channels. From there it entered the street drains, which carried wastewater out of the city. Inspection openings were built along the entire length of the drainage system. These allowed the channels to be cleaned and the system maintained. The network was designed so that wastewater flowed naturally by gravity. In the end, the waste was directed into special settling tanks or discharged into nearby rivers. Water played a central role in the life of the Indus Valley cities. Every city had numerous wells. In Mohenjo-Daro alone, archaeologists have identified more than 700 wells. Many houses and neighborhoods had their own private wells, while others served the wider public. At the centers of Harappan cities stood large pools often described as public baths. However, they likely served not only hygienic purposes, but also ritual ones. These pools were almost always located near the citadel that rose in the center of the city. What was the citadel of a Harappan city? It was a large stone or brick structure built on a natural or artificial mound. Inside the citadel were granaries, as well as an altar where a sacred fire was kept burning and sacrifices were offered. It's easy to imagine how these rituals may have taken place. People would gather for religious ceremonies, perform ritual bathing in the large pool, and then proceed to the citadel where the rites were carried out. These ablutions likely served to maintain ritual purity before taking part in the ceremonies. Most Harappan cities were surrounded by high walls. However, these walls did not serve a purely defensive purpose. The same appears to be true of the citadels in the centers of the cities. All of the evidence suggests that Harappan society was relatively peaceful. Archaeologists rarely find weapons at these sites. Many bronze daggers have been discovered, but such tools could easily have been used for everyday tasks. At the same time, archaeologists almost never find weapons designed specifically for warfare. Harappan sites contain no swords, and depictions of spears or bows are extremely rare. Finds of armor, helmets, or shields are also absent. In the material remains of other Bronze Age civilizations, all of these appear quite frequently. Despite the absence of a unified state, this civilization consisted of a large network of cities that coexisted without constant warfare. Around them lived tribes of hunter-gatherers, but they could hardly pose a serious threat to a large agricultural civilization. Farming societies had far larger populations than any hunter-gatherer groups. For this reason, the city walls likely served a different purpose. They protected the cities from floods. The Indus and Saraswati rivers regularly overflowed their banks, and even today the water level of the Indus during floods can rise by 5 to 7 meters, and in ancient times these floods were probably even stronger. The walls helped hold back the water and prevent it from flooding the city. Even so, floods sometimes broke through, something clearly visible in the archaeological layers. The citadels in the centers of the cities served a similar function. They were built on elevated ground to protect the granaries from flooding. Even if water flooded part of the city, the grain supplies would remain safe. But the achievements of the Harappans were not limited to hydraulic engineering. The Indus Valley civilization also stood out for its remarkable economic diversity. Archaeological excavations show that craftsmen of different trades often lived close to one another, forming what were essentially specialized craft districts. In Harappa, archaeologists have uncovered entire areas where jewelers worked. Thousands of unfinished items and large amounts of waste from the processing of precious stones have been found there. In other places, researchers discovered workshops belonging to metalworkers, weavers, and tailors. Harappan jewelers deserve special mention. They worked with agate, gold, silver, copper, and even glass. Particularly prized were beads made from carnelian, a semi-translucent stone with a deep red-orange color. The stone was cut into smaller pieces, holes were drilled through them, and the surfaces were carefully polished. Craftsmen then applied designs using a white paste and heated the beads. During firing, the pattern fused with the stone and became permanent. These ornaments were so popular that archaeologists have found them far beyond the borders of the Indus Valley civilization, for example, in Mesopotamia and East Africa. Urbanization here never reached the same scale as in Mesopotamia. Archaeologists have identified more than a thousand cities and settlements belonging to the Harappan civilization. That is far more than in Sumer, Akkad, and Assyria combined, and that's even if we include Mitanni and Elam. Yet large urban centers were relatively rare. The largest cities of the Indus Valley civilization, such as Mohenjo-daro, Harappa, Dholavira, and Rakigurhi, had populations of a few tens of thousands. By comparison, Mesopotamian cities such as Ur, Uruk, and Kish may have had more than 100,000 inhabitants at their peak. While in Mesopotamia, much of the population lived in cities, in the Indus Valley civilization, most people lived outside them and worked in agriculture despite the large number of urban settlements. The cities served as centers of craft production and trade, and their prosperity depended entirely on harvests from the surrounding lands. Harappan farmers cultivated wheat and barley, peas and lentils, sesame and millet, melons and dates. Cotton was especially important. The Harappans were the first people in the world to cultivate and process it. This is remarkable, since cotton cannot be eaten. Its only practical use is for making textiles and clothing. In other words, they were growing something not for survival, but for comfort and appearance. It may have been one of the earliest industries devoted purely to improving quality of life. Animal husbandry also played an important role in the economy. The Harappans domesticated water buffalo and zebu cattle, raised sheep, goats, pigs, and poultry. It did not yet have horses, though. Goods were transported in carts pulled by oxen. Some scholars suggest that they may have tamed elephants, though direct evidence for this is still lacking. Grain formed the basis of their diet. Wheat, barley, and millet were used to make bread and porridge. Meat was eaten less often, mainly mutton, goat meat, and beef. Food was cooked in clay pots over open fires. The remains of cooking hearths have been found in almost every house. Men usually wore a loincloth or a short skirt, sometimes with a cloak resembling a sarong. Women wore long skirts and shawls. Harappans were very fond of jewelry. Both men and women wore bracelets made from shells, ivory, copper, gold, clay, and stone. In their free time, they played games. Archaeologists have discovered gaming dice similar to modern ones, as well as game boards with small depressions. Children played with clay toys, usually small figurines of animals and people. The Harappan civilization did not exist in isolation. It was part of a vast trade network that connected South Asia with Central Asia, Iran, and Mesopotamia. Mesopotamian written sources repeatedly mention a land called Meluha. Most scholars identify it with the Indus Valley civilization. Texts from the late 3rd millennium BC often refer to ships from Meluha arriving at Mesopotamian ports carrying exotic goods such as ivory, pearls, and spices. The Harappans also exported semi-precious stones, timber, especially valuable hardwoods, and a wide range of crafted goods. Trade took place both over land and by sea. Overland caravans traveled through Balochistan into Iran and from there through Elam to Mesopotamia. The maritime route passed through the Persian Gulf. Ships from Meluha stopped in Dilmun on the island of modern Bahrain and from there continued to the ports of southern Mesopotamia. The Harappans were skilled sailors. In the city of Lothal, one of the southernmost centers of the civilization, archaeologists discovered what may be the oldest dockyards in the world. It consisted of a large basin connected to the river by a system of sewage gates. At high tide, water filled the dock and ships could enter. The gates were then closed allowing vessels to remain afloat even when the tide went out. When necessary, the water could be drained, making it possible to repair ships or carry out other work. From Lothal, Harappan ships sailed along the coast of present-day Pakistan and then continued along the shores of Oman toward the Persian Gulf and Dilmun, where from there to the ports of southern Mesopotamia. There is also evidence suggesting that the maritime journeys may have reached even farther. On the coast of East Africa, particularly in what is now Somalia, archaeologists have discovered Harappan seals and other artifacts from this civilization. One such seal was even found on the island of Zanzibar. This suggests that Harappan sailors may have reached these distant shores. To support trade, the Harappans developed a system of standardized weights used across the entire territory of the Indus Valley civilization. Archaeologists have uncovered numerous stone cubes of different sizes, each corresponding to a specific unit of weight. The smallest unit was about 0.856 grams, and larger weights followed a regular sequence, 2, 4, 8, 16, 32, and so on. This system allowed merchants to weigh both small and large quantities with great precision. What is especially notable is that these standards were identical across the entire civilization, from Harappa in the north to Lothal in the south. This points to a high level of organization and the widespread use of unified trade standards. These standards were not limited to the Indus Valley itself. Harappan weights have also been found beyond its borders, and they were widely used in places such as Dilmun and Elam. Now let us turn to writing. If we're dealing with the Indus Valley civilization, it's reasonable to expect that it had its own writing system. After all, writing is one of the key features of a civilization, and indeed such a system existed. So far, archaeologists have discovered nearly 20,000 inscriptions written in the Harappan script, containing more than 400 distinct signs. The symbols include images of people, animals, plants, geometric shapes, and abstract marks. The Harappans wrote from right to left. This can be seen in many inscriptions where the symbols appear compressed toward the left side, as if the scribe was running out of space and made the final sign smaller to fit the entire text. Yet despite the large number of inscriptions that have been found, the meaning of these symbols remains unknown. Scholars have not yet been able to determine the phonetic value of even a single sign. More than 60 attempts have been made to decipher this script. Notably, no two attempts have produced the same result, and this suggests that a reliable solution to the problem is still far away. The main difficulty lies in the length of the texts. Most inscriptions contain only five to seven signs. The longest known text consists of just 26 symbols. For a full decipherment, this is extremely little material to work with. It is possible that the Harappans wrote not only on clay tablets or seals, but also on other materials. In the Harappan city of Dholavira, archaeologists uncover the remains of a wooden board bearing signs of the Indus script. Each symbol was about 37 centimeters tall. This discovery suggests that the Harappans did not write exclusively on clay. Clay simply survives much better over time, whereas wood or other materials usually decay. The presence of this inscription also points to a relatively high level of literacy among the population, since the board was most likely placed in a public location where many people could see it. There is still hope that a bilingual inscription will one day be discovered, written on one side in the Harappan script, and on the other a language we already understand, such as Sumerian or Akkadian. The chances are not impossible, since the Harappans traded extensively with Mesopotamia. In the past, discoveries like this often have provided the key to deciphering unknown languages and writing systems. The Behistun inscription, for example, became the key to deciphering cuneiform, while the Rosetta Stone allowed Jean-Francois Champollion to decipher Egyptian hieroglyphs. Incidentally, in 2025, the government of the Indian state of Tamil Nadu announced a reward of $1 million for anyone who can decipher the Indus script. If you're interested in history, linguistics, or ancient languages, this might be your chance. Imagine trying to understand Christianity without the text of the Bible, without a single intact church, and without a single written prayer. All you have are a few small figurines, poorly painted icons, and perhaps the remains of burned candles. This is roughly the situation researchers face when trying to reconstruct the religion of the Indus Valley civilization. Yet, a closer look reveals far more than it might seem at first. Almost every other civilization left behind a religion that's impossible to overlook. Egypt left enormous temples, lists of gods, and detailed descriptions of the afterlife. Mesopotamia left ziggurats, the Epic of Gilgamesh, and thousands of tablets containing prayers and rituals. Even much smaller cultures usually leave behind something that clearly reflects their beliefs. The Harappan civilization, however, remains largely silent. No temples have been found, and no royal burials filled with offerings to the gods. Thousands of seals bear inscriptions, but we still cannot read them. It is possible that the names of their gods have already been discovered, we simply do not yet realize it. For a civilization that lasted for millennia, and whose cities were home to millions of people, the silence is remarkable. But silence does not mean that they believed in nothing. Look at their cities. At the center stands the citadel, and beside it a large pool. Special stairways led down to it, and the walls were carefully sealed to prevent water from leaking out. Clearly, this structure had special significance. It was likely used for ritual bathing. For Harappans, cleanliness was not merely a matter of hygiene, but also had a sacred meaning. Before approaching the sacred fire at the altar in the citadel, before taking part in a ritual, a person likely had to purify themselves with water. Both body and soul had to be clean. If this idea sounds familiar, that is not a coincidence. It lies at the heart of many practices in Hinduism, which developed much later. Ritual bathing in the Ganges, ideas of ritual purity and impurity, and the tradition of cleansing before prayer are still present in Indian culture today. It is quite possible that the roots of these beliefs reach back to the Harappan civilization. And now about fire. On the altars of the citadels, a sacred fire burned continuously. This is not speculation, but a fact confirmed by the analysis of soot on the bricks and stones from which these altars were built. The fire was kept burning constantly, and rituals of complete offering were performed there, sacrifices entirely consumed by the flames. Grain, food, animals, all of these burned on those altars for centuries. It is striking that many centuries later, when the Indo-Aryans entered the Indus Valley, fire also held a central place in their religion. Vedic rituals were inseparably connected with fire. Agni, the god of fire, became one of the most important deities of the Vedic pantheon. In Iran, this tradition later developed into Zoroastrianism with its cult of the sacred fire that must never be extinguished. Do the Indo-Aryans adopt this cult from the peoples they encountered in the Indus Valley? It's difficult to prove, yet it's hard to dismiss the possibility that the fires burning on those ancient altars ignited something greater than the sacrifices themselves, perhaps an entire religious tradition. Now let's look at the seals. Among the thousands that have been discovered, one scene appears so often that it can hardly be a coincidence. It depicts a figure sitting with legs crossed in a posture that today we call the lotus pose. Around the figure are animals, an elephant, a tiger, a rhinoceros, and a buffalo, and on the head are large horns. Who is this figure? We don't know the name, but researchers have noticed an intriguing parallel. Roughly 2,000 years after the decline of the Harappan civilization, the god Shiva appears in Indian tradition. He too is depicted in a meditative posture, and he is associated with wild animals and regarded as their lord. Is the Harappan figure a direct ancestor of the image of Shiva? That is impossible to prove, yet the resemblance is striking enough that it is difficult to ignore. It is possible that we are looking at one of the earliest representations of a deity that would later become one of the most revered in the world. Among the archaeological finds, there are also many female figurines with deliberately emphasized full forms. In ancient cultures, such figures are often associated with a fertility goddess, the earth that produces crops, the mother who gives life. This idea is likely as old as agriculture itself, and in this respect, the Harappans were no different from many other ancient cultures. But there is one detail worth noting. In some images, researchers believe they can identify scenes that may represent human sacrifice. This does not necessarily mean that the Harappans were especially cruel. In the ancient world, sacrifice was often understood as the highest act of devotion to the gods, a way to maintain balance between the human and the divine worlds. Still, it reminds us that the religion of this civilization, like many others in antiquity, may also have had a darker side. But perhaps the most interesting thing is not what exactly they believed, but how they expressed those beliefs. There are no pyramids built in honor of the gods, no grand temples, and no inscriptions praising a ruler as a messenger of heaven. Instead, we see orderly houses of roughly similar size, a large pool at the center of the city, and an eternal fire burning on the altar in a citadel. If other civilizations proclaimed their devotion to the gods through monumental architecture and grand displays, the Harappans seemed to have approached the divine more quietly, through water, through fire, and through the daily purification of the body. And perhaps, through the posture of a person sitting motionless, eyes closed in complete silence. Today, we call this meditation. Between 2600 and 1900 BC, the Indus civilization reached the peak of its development. It covered a territory of more than one and a half million square kilometers, around 580,000 square miles. This was an enormous area. If we compare it with all the other major civilizations of the time, Egypt, Mesopotamia, and China, even combined, they occupied less territory than the Harappan civilization. Across this vast region lived more than five million people. What could possibly destabilize such a massive civilization? For a long time, scholars believed that the Harappan civilization collapsed because of an invasion by Indo-Aryan tribes who arrived from the north. This hypothesis was based on several observations. First, the Indo-Aryans did indeed appear in the Indus Valley around 1500 BC. Second, the Rig Veda, one of the earliest Indian texts composed around that time, describes the struggle of Aryan gods against fortified cities and the dark-skinned inhabitants of these lands. Today, however, this theory is no longer widely accepted among researchers. Most importantly, it lacks archaeological support. Archaeologists see no signs of large-scale destruction or warfare. There are no mass graves of victims. There are no sudden shifts in material culture that one would expect after a conquest. In addition to this, the chronology does not match either. Archaeological evidence shows that the decline of the Indus Valley civilization began two to three centuries before the Indo-Aryans arrived in the region. By the early second millennium BC, the quality of architecture, crafts, and trade had already begun to deteriorate. From around 1700 BC onward, Mesopotamian sources almost stopped mentioning merchants and goods from Meluha. This suggests that when the Indo-Aryans entered the region, they encountered only the remnants of the Harappan civilization, which was already in decline. One could say that the arrival of new tribes merely completed a process that had already begun. This raises the question, what actually caused the collapse? Today, an increasing number of researchers believe that the inhabitants of the Indus Valley may, to a significant extent, have contributed to their own decline. All of their major cities and structures were built from brick. However, unlike Mesopotamia, where builders mainly relied on sun-dried mud brick, the Indus Valley civilization widely used fired brick. This made perfect sense, since fired bricks are far stronger and more durable. In Mesopotamia, mud brick was used not because people were unaware of the advantages of fired The region had very few forests, and firing bricks requires large amounts of fuel. As a result, many Mesopotamian buildings used fired bricks only for the outer facing, while the main body of the walls was constructed from sun-dried mud brick. The Harappans, however, had access to forests and made extensive use of wood to fire their bricks, To produce the enormous quantities of brick required for their cities, they cut down more and more trees. This didn't happen suddenly, but over time it led to widespread deforestation across the region. As a result, floods from the Indus and Saraswati rivers became far more destructive. Previously, vegetation had at least partially slowed the flow of water, but once the forests were cleared, this natural barrier disappeared. Floods began to cause much greater damage. Most importantly, tree roots no longer held the soil in place. During seasonal floods, rivers began to wash away the fertile topsoil. This reduced agricultural productivity and led to soil salinization and long-term land degradation. At the same time, the processes of aridization that had once helped give rise to this civilization continued to intensify. The climate grew steadily drier, monsoon rains weakened, and the region experienced more frequent and prolonged droughts. In earlier periods, fertile soils and well-developed irrigation systems had allowed the Harappans to endure such conditions relatively easily, but once the land had begun losing its fertility, this became far more difficult. Harvests declined, and the population gradually began to shrink. Another blow came from the natural changes in the river system. The Indian subcontinent is a region of significant seismic activity because it continues to move northward and collide with the Eurasian landmass. As a result of tectonic shifts, the course of the Indus changed, while the Saraswati River disappeared altogether. For a civilization that depended entirely on rivers and irrigation, this was a catastrophe. For people who regarded the Saraswati as a sacred river, its disappearance meant more than a loss of water, it meant that the gods had turned away from them. As a result, the Harappan civilization gradually declined. It didn't disappear overnight, but by the time the Indo-Aryans arrived, only its remnants remained. The population began leaving the Indus Valley. Some groups moved east into the Ganges Valley, where forests still survived and the climate was far more favorable for agriculture. Rice cultivation was expanding there at the time, and it was far more productive than wheat, barley, or millet. Another large portion of the population migrated south to the Indian subcontinent. According to current theories, the Tamils and other peoples who speak Dravidian languages may be descendants of the population of the Indus Valley civilization. Increasingly, in what is now Pakistan, Afghanistan, and Iran, there still lives a people known as the Rahui, who speak a Dravidian language. It is possible that they preserve part of the linguistic heritage of the ancient inhabitants of the civilization. Despite its decline, the Harappan civilization did not disappear without a trace. Agricultural practices, metalworking technologies, and various crafts continued to exist and later were adopted by other peoples, including the Indo-Aryan tribes that arrived from the north. There is also a strong possibility that certain elements of Harappan culture influenced the development of later Indian traditions. These may include the cult of the sacred cow, ritual purification with water, and perhaps even some of the practices associated with yoga. Many features that today are associated with Hinduism may ultimately trace their roots back to the Harappan civilization. However, proving this remains extremely difficult, largely because its writing system has not yet been deciphered. For more than 3,000 years, the ruins of Harappan cities laid buried beneath the earth. Local people sometimes came across strange objects, but they didn't understand where they came from. In Harappa itself, villagers spent centuries dismantling ancient brick structures and reusing the bricks for their own needs. When the British built the railway, they even used thousands of Harappan bricks as ballast and as a foundation for the tracks. No one realized their true value. It reminds us that beneath the ground we walk on lies thousands of years of human history. If you made it to the end of this video, we really appreciate it if you liked and subscribed. Follow along on our journey through ancient civilizations in history. If you'd like to support the channel, join our Patreon or become a YouTube channel member. You get early access to new episodes, behind-the-scenes looks, and more. You can also leave a super thanks below to give us a little extra boost. If you want to listen to history on the go, check out our all-new podcast Parabellum History. You can find it on all major podcast platforms. Thanks again for tuning in, and we hope to see you next time.