The Harappan Civilization of South Asia, ca. 2500 to 1900 B.C.E., was a period of intense urbanization. In the archaeological record, a unique assemblage of material artifacts represents this culture. We first see this assemblage and urbanization in the Indus Valley ca. 2500 B.C.E. It spreads widely, and suddenly disappears six centuries after its first appearance. After six centuries of use and massive economic investment, why were these cultural norms abandoned? Why a sudden and complete abandonment?

Archaeologists have proposed numerous models to explain the collapse of the Harappan Civilization. Floods, invasions, earthquakes, and climatic change have all been proposed as answers. I do not believe that any current proposal is completely convincing. The evidence for each is limited to a single small area or locality, and is then imposed as a universal answer upon the entire civilization.

In an attempt to answer the question of why the Harappan Civilization collapsed, I will first give a brief summary of the Harappan Civilization. Next, I will describe what is meant by collapse and what portions of society ‘collapsed.’ Third, I will summarize the four primary hypotheses previously proposed. Finally, I will attempt to synthesis a new and broader hypothesis to explain the collapse of the Harappan Civilization

At the same time as the Old Kingdom of Egypt and the Early Dynastic Period of Mesopotamia, an extensive and complex civilization dominated South Asia. Called the Harappan Civilization, it extended temporally from 2500 to 1900 B.C.E. A time of homogenization, exemplified by the adoption of a particular artifact assemblage. This assemblage included: a single unique script, a recognized and broadly utilized iconography, large buildings of uniform baked brick, stoneware, broad use of copper/bronze, urban drainage systems, and broad use of the Harappan Decorated Ware.

The Harappan Civilization was located in northwestern South Asia. The primary core was located in modern Pakistan along the Indus River and its tributaries. The secondary settlement included the rest of Pakistan, and much of northwestern India, including: Gujarat, Punjab, Hary~na, and Rajasthan. Fingers of secondary and peripheral settlement extended along the Makran Coast, through the passes into Afghanistan, Iran, and Turkmenistan, along the Gangetic Plain half way through Uttar Predesh, and down the west coast of India as far as Mumbai.

The Mature Harappan was a time of intense economic and trade activities. These activities were supported by the extensive use of a uniform writing system, weights, and linear measures. The script was logographic in nature and contained more than 500 signs. This script appears to be unrelated to any other system and died with the collapse of the Harappan Civilization. The Harappans utilized a base eight system for numeration and a binary system for weights.

A complex system of trade networks made the Harappans rich and guaranteed access to exotic goods. Internal networks moved every imaginable good throughout the Civilization. Shell, dried fish, and pearls from the coast; copper, tin, chert, precious metals and semiprecious stone from the hill country; and grain, animals, and wood from the rural areas flowed from one area to another, resulting in a nearly homogenous distribution of goods across the face of the civilization irrespective of origin. Networks extended into Central Asia, Mesopotamia, and the Arabian Peninsula. These networks exported every good and luxury available in the Harappan Civilization. It is unclear what was being imported, but it is likely to be wool cloth, fish, and grain.

The Harappan Civilization utilized a diverse assemblage of wild and domestic plants in the production of food and industrial products. Animal production centered on zebu cattle, buffalo, sheep, goats, fish, chicken, and some wild species. Agricultural foods were produced through two means of production. Crops of barley, wheat, oats, lentils, chick and grass peas, jujube, and mustard were sown in autumn, harvested in spring, and watered by winter rains. In the second, crops such as millits, sorghum, rice, cotton, and dates and were sown in the summer to be watered by the summer monsoon and harvested in the fall. As time passed the people of both areas diversified and intensified their food production by incorporating both techniques.

Urban centers of the Harappan Civilization were large and sophisticated. They were well planned with separate domestic and public space, each demarked into efficient areas of action. In domestic areas numerous wells, broad strait, streets, and an expansive system of public sanitation, are indicative of Harappan foresightedness and political control. Public areas were ritual and secular; each with its own designated location. Several areas of manufacture were designed for, the resident trades evidently were decided by the amount of pyroclastic activity necessary for completion of the good. Goods produced as a result of advanced craft activities and specialization include: complex stone beads, fine and coarse ceramics, copper/bronze tools, faience, seals, shell and clay bangles, clay figurines, stoneware. The Harappans developed fine and distinctive art: jewelry, masks, seals, stone and cast bronze sculpture, and ceramic figurines.

When we consider the reasons for the collapse of the Harappan Civilization, we must first define what did change and what, if anything remained static. Most basic to any culture are the people. Possehl reports a clear and consistent occupation of sites from the Mature through the Late Harappan (Possehl, 1982). The genetic evidence shows there was little population change early in the second millennium B.C.E. (Hemphill, Lukacs and Kennedy, 1991).

The deurbanization period of the Harappan Civilization saw the collapse and disappearance of the urban phenomena in the South Asia for the next seven centuries. The theme for this period is localization. Significant change in the cultural assemblage did occur. Architectural and ceramic forms changed along with the loss of writing, planned settlements, public sanitation, monumental architecture, seaborne and exotic trade. seals, and weights (McIntosh, 2002). At this time a small but visible population influx occurred from Afghanistan and Baluchistan. The continuation of local and regional polities from the Early through the Post Harappan seems evident; that which had integrated and united the area disappeared.

Archaeologists have offered four primary and competing explanations for the collapse of the Harappan Civilization. Three are based on ecological factors: intense flooding, decrease in precipitation, and the dessication of the Sarasvati River. The fourth hypothesis is that of the Aryan Invasion, proposed by Sir R. E. Mortimer Wheeler and Stuart Piggott (1953 and 1950). It was based on a diffusionary model of a mass invasion of Indo-Aryan peoples swarming into and destroying the civilized Harappan Civilization. There is no good evidence to support this conclusion: no destruction levels, mass graves, or large population change.

The first ecologically based model is that of flooding. First proposed by hydrologist Robert L. Raikes (1964), this model suggests that a natural dam developed to the south of Mohenjodaro near Sehwan. Raikes saw evidence for massive flooding at Mohenjodaro and proposed this model in response (Raikes, 1964). R. J. Wasson (1987 and 1987) argued that the unconsolidated alluvial sediments of the Indus floodplain would not have withstood the pressure of such extensive flooding.

The second and more widely supported model is that of desiccation caused by a decrease in precipitation. First proposed Sir John Marshall (1931) and later expanded by Wheeler (1953), the model was based not on some empirical measure of environmental change; but, upon a flowed analogy drawn from the archaeological evidence. They felt that the Harappan Civilization was a subset of a larger riverine group including Egypt and Mesopotamia (Possehl, 2002). Cultural traits, such as the extensive use of baked brick instead of mud brick, elaborate civic drainage systems, and wet environment animals (elephants, tigers, rhinoceri) represented on art and seals were considered proof of a wetter environment than today (Possehl, 2002).

G. Singh (1971) proposed environmental evidence in support of the ‘dessication hypothesis’. He looked at the changing salinity of three lakes in Rajasthan, India as expressed in pollen cores. He saw a salinity increase in the beginning of the second millennium B.C.E. (Singh, 1971). From this he deduced a precipitation decreases and proposed this decrease as the primary contributing factor in the collapse of the Harappan Civilization. Currently both saline and fresh water lakes dot the Rajasthan landscape (Possehl, 2002). The salinity of such lakes are determined by the amount of subterranean drainage (Possehl, 2002). Whether these drains are open and allow salinated water to flow out or are closed and allow only evaporation is controlled by the plate movements (Possehl, 2002). A number of additional studies have reported similar results and proposed similar hypotheses (Bryson and Swain, 1981 and Vishnu-Mittre and Sharma, 1978). In opposition, several studies have found no reason to consider any desiccation of the environment (Raikes and Dyson, 1961 and Possehl, 2002).

In conclusion, the Harappan Civilization was not a vase, containing all the bits which define a culture but broken before our arrival where all we must do is decide whether it fell off the table or if some idiot with a hammer came along and smashed it to pieces. The civilization was the complex actions of living, breathing people. What would stop people from acting one group of behaviors in favor of another group, at the same time across most of the civilization? Any answer must have a causal relationship with the collapse and a means by which the effect was both sufficient and necessary.

I will propose a model in which the collapse of the Harappan Civilization occurred in three phases. First, the highly integrated and productive Harappan economy collapsed due to severe disruption of the its agricultural base. Second, this collapse severely disrupted the support structure of the elite population. These elites were responsible for the imposition of the Harappan Cultural Assemblage. As these elites disappeared so did the Harappan Civilization.

Sometime between 1900 and 1750 B.C.E., a sever earthquake occurred. It was centered somewhere in northeastern India. The tectonic uplift associated with this occurrence caused two rivers to shift their courses. The Sutlej shifted from the Sarasvati drainage to the Indus. And the Yamuna shifted west from the Sarasvati to the Ganges. The Sutlej and the Yamuna were two of the three primary feeder rivers for the Sarasvati. Their loss resulted in the desiccation of the once large river to its current state as a small stream and buried riverbed. During the Mature Harappan Period, the Sarasvati watered half the Harappan cities, settlements, and agricultural fields. Its loss would have constituted a major disruption of the Harappan economy.

This earthquake had other effects on the Harappan Civilization and its economy. Despite the limited nature of the Raikes Flood Hypothesis, the signs of an extreme depositional event are compelling. The shift west of the Sutlej River would have resulted in a massive flood event which would have scoured silt from the riverbeds and flood plains of upper Sind to be deposited along bends and in the Indus Delta. This flood would have been a single extreme event which would have destroyed much river infrastructure and thus further disruption of the Harappan economy.

In Rajasthan, the population was centered around precipitation fed lakes. We have already seen that the salinity of these lakes is dependant on the available drainage. The available drainage can and is regularly changed as a result of tectonic action. At the same time as the earthquake in northwest India, the salinity levels in some Rajasthan lakes began changing. At the same time, there is no evidence for any change in precipitation. The change in lake salinity would have forced population movements. Though these movements would have been small scale and over short distances, it would have further disrupted the Harappan economy.

How does this disruption and collapse of the Harappan economic system result in the collapse of the entire civilization? To this end we must first look at the culture in terms of a set of interdependent systems, each with its own input and output. This gives us a fairly accurate model of how the civilization functioned. This functional approach has in the past been unable to account for change in the model, this is no longer true with the application of stability theory.

William Baden, in his research on the Mississippians, has applied new methodology to the functional approach in the form of stability theory. Stability theory is often used to predict the reactions of aero and hydrodynamic flow in mechanical systems. When applied to cultural systems it is used to explain change (Baden, 1995). Change is the result of any system instability system, thus cultural systems can be viewed as the function of stability verses instability (Baden, 1995). Through a process of morphogenesis new cultural phases evolve in response to fluctuations in the cultural system (Baden, 1995).

How does this apply to the Harappan Civilization? Increasing systemic instability would result from the massive disruptions in the Harappan economy. From game theory we know that individuals act in support of both stability and instability. The more unstable the system becomes the more people would act for stability. In an unstable environment, stability would offer the greatest return potential.

Where would these people unconsciously seek stability? Before the advent of the Harappan Civilization, the northeast South Asia was covered with numerous smaller polities which lasted for many centuries. With the imposition of Harappan culture by an elite population, these polities did not disappear. They continued much the same as before, but with a veneer of Harappan culture. It was the Harappan trade based economy that was disrupted, not the previous subsistence economy. Cities were abandoned with an increase of rural sites in some areas. The local goods known from the Pre-Harappan and continuing through the Mature Harappan, became the primary assemblage of many areas of northwest South Asia at the end of the Harappan Civilization. It seems that the non-elite Harappan population went back to what it had been doing before the advent of Harappan Civilization.

The elite population lost power. This loss resulted in an abandonment of Harappan culture traits which hade been imposed on local populations. Many Harappan cultural traits, such as writing and extensive trade had positive effects on the lives of individuals, others had involved massive investments of time and material, so why were they abandoned to the detriment of these same people. I propose that these populations abandoned everything Harappan in a response to a complete loss of legitimacy of the Harappan elites. As these individual populations localized, they distinguished themselves from the Harappans by refusing those cultural traits most associated with the old elites, writing, urbanization, seals, etc.