The Indus Valley Civilization was one of the earliest urban cultures in South Asia, flourishing around 3300-1300 BCE along the Indus River valley. Two major sites are Harappa and Mohenjo-Daro, which had sophisticated sewage and water systems including covered drains and wells. The cities followed a grid pattern and many homes had bathing areas. The civilization declined around 1300 BCE for unknown reasons but left lasting impacts on the region.