In 1921, archaeologist’s uncovered evidence of an ancient civilization along the Indus River, which today runs through northwest India into Pakistan. The so-called Indus Valley civilization (also known as the "Harappa civilization" for one of its chief cities) is thought to have originated as early as 7000 BC and to have reached is height between 2300 to 2000 BC, at which point it encompassed over 750,000 square miles and traded with Mesopotamia. The Indus Valley people were most likely Dravidians, who may have been pushed down into south India when the Aryans, with their more advanced military technology, commenced their migrations to India around 2,000 BCE. Though the Indus Valley script remains undeciphered down to the present day, the numerous seals discovered during the excavations, as well as statuary and pottery, not to mention the ruins of numerous Indus Valley cities, have enabled scholars to construct a reasonably plausible account of the Indus Valley Civilization.

        The Indus Valley civilization raises a great many, largely unresolved, questions. Why did this civilization, considering its sophistication, not spread beyond the Indus Valley? In general, the area where the Indus valley cities developed is arid, and one can surmise that urban development took place along a river that flew through a virtual desert. The Indus Valley people did not develop agriculture on any large scale, and consequently did not have to clear away a heavy growth of forest. Nor did they have the technology for that, since they were confined to using bronze or stone implements. They did not practice canal irrigation and did not have the heavy plough.

Indus River

         Most significantly, under what circumstances did the Indus Valley cities undergo a decline? The first attacks on outlying villages by Aryans appear to have taken place around 2,000 BCE near Baluchistan, and of the major cities, at least Harappa was quite likely over-run by the Aryans. In the Rig Veda there is mention of a Vedic war god, Indra, destroying some forts and citadels, which could have included Harappa and some other Indus Valley cities. The conventional historical narrative speaks of a cataclysmic blow that struck the Indus Valley Civilization around 1,600 BCE, but that would not explain why settlements at a distance of several hundred miles from each other were all eradicated. The most compelling historical narrative still suggests that the demise and eventual disappearance of the Indus Valley Civilization, which owed something to internal decline, nonetheless was facilitated by the arrival in India of the Aryans.

         Indus River, Tibetan and Sanskrit Sindhu, Sindhi Sindhu, or Mehran,  great trans-Himalayan river of South Asia. It is one of the longest rivers in the world, with a length of some 1,800 miles (2,900 km). Its total drainage area is about 450,000 square miles (1,165,000 square km), of which 175,000 square miles (453,000 square km) lie in the Himalayan ranges and foothills and the rest in the semiarid plains of Pakistan. The river’s annual flow is about 272 billion cubic yards (207 billion cubic metres) twice that of the Nile River and three times that of the Tigris.