The Indus Valley civilization was centered round the Indus River in India and Pakistan, and is the earliest known urban culture of the Indian subcontinent. Superimposed on earlier stone- and bronze-using cultures dating from c.4000 BC, the Indus Valley civilization centered around Harappa and Mohenjo-Daro, and lasted from c. 2500 to c. 1750 BC. About 100 of its towns and villages, some with fortified citadels, have been identified.