The Harappan civilization was mainly urban and mercantile. Inhabitants of the Indus valley traded with Mesopotamia, southern India, Afghanistan, and Iran for gold, silver, copper, and turquoise. The Mesopotamian model of irrigated agriculture was used to take advantage of the fertile grounds along the Indus River. Earthlinks were built to control the river's annual flooding. Crops grown included wheat, barley, peas, melons, and sesame. This civilization was the first to cultivate cotton for the production of cloth. Several animals were domesticated including the elephant which was used for its ivory.
Most of the artwork from this civilization was small and used as personal possessions. The first objects unearthed from Harappa and Mohenjo-Daro were small stone seals. These seals were inscribed with elegant portrayals of real and imagined animals and were marked with the Indus script writing. The seals suggest a symbolic or religious intent. Stone sculptures carved in steatite, limestone, or alabaster depict a male figure who may have represented a god. Pottery figures were shaped into humans and animals. Very few bronze figures have been recovered.
The Harappan civilization experienced its height around 2500 BC and began to decline about 2000 BC. The causes of its downfall are not certain. One theory suggests that warlike Iranian Nomads with spoke wheeled chariots from the Volga River Valley area migrated into this area. Iranian religious texts and human remains in Mohenjo-Daro suggest that the Iranians may have violently entered the area, killing its inhabitants and burning the cities.
However, another theory supported by more recent evidence suggests that this civilization may have begun to decline before the Iranians arrived. The inhabitants of the Indus valley dispersed before the Iranians slowly entered the area as a nomadic people. The Iranians were then able to take over this area since most of the inhabitants had previously left. One cause of the dispersal of the Harappans could have been a result of agricultural problems. Topsoil erosion, depletion of nutrients from the soil, or a change in the course of the Indus River may have forced these people to leave their towns and move northeastward in search of more fertile land.