The Indus Valley Civilisation (IVC), also known as the Harappan Civilisation, is a Bronze Age urban civilisation and one of the three earliest and most widespread ancient civilisations, alongside ancient Egypt and Mesopotamia. It originated in the alluvial plain of the Indus River and the Ghaggar-Hakra river basin, spanning modern-day Pakistan, northwestern India, and northeast Afghanistan. The civilisation lasted from approximately 3300 BCE to 1300 BCE, with its Mature Harappan Phase flourishing between 2600 BCE and 1900 BCE. Its discovery in the 1920s at sites like Harappa and Mohenjo-daro moved the timeline of Indian civilisation back by over a millennium.
The IVC is characterized by its advanced urban planning. Major cities were laid out on a precise grid pattern with streets intersecting at right angles. Construction utilized standardized baked bricks in a consistent ratio across different sites. A key mechanism was the sophisticated public health infrastructure, including a system of covered drainage systems that connected individual houses to main street sewers, and public structures like the Great Bath at Mohenjo-daro. The economy was based on agriculture and extensive trade, including long-distance sea trade with Mesopotamia.
The IVC connects to the subsequent Vedic Civilisation, which emerged a few centuries after the Harappan decline, with ongoing research exploring the cultural relationship between the two periods. Recent archaeological findings have significantly changed the understanding of the IVC. New radiocarbon dating at sites like Bhirrana in Haryana has pushed the antiquity of some settlements back to the 8th millennium before present, suggesting the IVC may be older than the Egyptian and Mesopotamian civilisations. The theory for its decline has shifted from the discredited "Aryan Invasion Theory" to a gradual transformation caused by climate change, a drying of the region, and changes in cropping patterns.