The Indus Valley Civilization evolved in the Bronze Age civilization. It was located in the northwestern region of the Indian Subcontinent. This civilization primarily flourished around the Indus River basin concentrated more along the Indus and the Punjab region, extending into the Ghaggar-Hakra River valley and the Ganges-Yamuna Doab.
Geographically, the civilization was spread over an area of some 1,260,000 km. This made it the largest ancient civilization in the world. The Indus Valley is one of the world's earliest urban civilizations, along with its contemporaries, Mesopotamia and Ancient Egypt. When this civilization reached the peak of its glory, it boasted of a population of over five million.
Inhabitants of the ancient Indus river valley developed new techniques in metallurgy and handicraft. They produced copper, bronze, lead, and tin. The civilization was extremely popular for its cities built of brick, roadside drainage system, and multistoried houses.
The mature phase of this civilization was known as the Harappan Civilization. This was because the first of its cities to be unearthed was the one at Harappa. This was excavated in the 1920s in the then Punjab province of British India which is located in the present day Pakistan.
Archeological excavations of Harappan sites have been ongoing since 1920. Significant discoveries, however, occurred recently in the year 1999. Till date, over 1,052 cities and settlements have been found. These settlements were mainly in the general region of the Ghaggar-Hakra River and its tributaries.
Among the settlements were the major urban centers of Harappa, Lothal, Mohenjo-daro which was declared as the World Heritage Site by UNESCO. Among the others were, Dholavira, Kalibanga, and Rakhigarhi.
The civilization is also sometimes referred to as the Indus Ghaggar-Hakra civilization or the Indus-Sarasvati civilization. The title Indus-Sarasvati was based on the possible identification of the Ghaggar-Hakra River with the Sarasvati River. This Sarasvati River belonged to the Nadistuti sukta in the Rig Veda. However, this usage is disputed on linguistic and geographical grounds.
The Harappan language is not directly attested and its affiliation is unknown. This would be a plausible relation to Proto-Dravidian or Elamo-Dravidian.
It was almost 700 years later that the Harappan cities began to decline. There are many reasons for its decline. However, till today it remains more of a mystery, yet according to many scholars and historians the invasion of a foreign people was the prime reason for its decline.
However, according to Kenoyer and many other such archaeologists the decline of the Indus cities was a result of many factors. These included the overextended political and economic networks, the drying up major rivers etc to name a few. These all contributed to the rise of a new social order.
In fact, there is also archaeological evidence indicating that around the late Harappan phase, from 1900-1300 B.C. the city was not being maintained and was getting crowded. This suggested that the rulers were no longer able to control the daily functioning of the city. Having lost authority, a new social order rose up.