The prehistoric period (2500 to 1800 BCE)

Urbanization in the Indian subcontinent dates back to 2500 BCE. The Indus valley region was the seat of this pre-historic urban civilization. Named after the first site that was excavated in Harappa, the Harappan civilization was primarily urban though the people were agricultural. Of all the sites that have been excavated so far, Mohenjodaro and Harappa are regarded as the two most important cities of this civilization. Lothal was a major port in the Gulf of Cambay. It is estimated that the Harappan cities had about 35,000 inhabitants.

Mohenjodaro and Harappa were both situated on the banks of navigable rivers and the cities consisted of two parts: the citadel, located on high ground and the lower city where the quarters of the ordinary people were located. The lower city was built on a grid pattern. The cities had excellent covered drainage system with manholes for periodic cleaning. Soak-pits partially purified the sewage before draining them into the river. Brick-lined wells provided water to homes. Houses built with fired bricks of uniform size could boast of basic urban amenities such as baths and toilets.