Indus Valley at its Peak
Around 2500 BCE, the Indus Valley, or Harappan, civilization was entering its mature phase, with cities, towns and villages spread across a vast area of what is now Pakistan, northwest India and parts of Afghanistan. Estimates of its extent often run to around a million square kilometers, which would make it larger than contemporary Egypt or Mesopotamia. It matters because it was one of the world's first urban societies, and because it achieved this scale with a way of life that looks strikingly different from its neighbors.
The civilization grew out of earlier farming communities in the Indus plains and surrounding uplands, which had been cultivating wheat and barley and herding cattle for thousands of years. Fertile floodplains fed by the Indus and other rivers, including the now-dried Ghaggar-Hakra system, supported growing populations. By roughly 2600 BCE, scholars see a shift toward planned towns, standardized goods and long-distance exchange. The dates for the "mature" phase vary somewhat, with most placing it between about 2600 and 1900 BCE.
The great cities, notably Mohenjo-daro and Harappa, are the best-known expressions of this peak. They were laid out on grid-like street plans, built with fired and mud bricks of consistent proportions, and equipped with remarkable drainage systems, wells and private bathing areas. Archaeologists have found standardized stone weights, finely made beads, pottery and carved stone seals bearing animal motifs and short inscriptions. The script has never been deciphered, so the language and many aspects of Harappan belief and politics remain unknown. Other major sites include Dholavira, Ganweriwala and Rakhigarhi, and the port-like settlement of Lothal suggests maritime links. Harappan goods turn up in Mesopotamia, which names a trading partner called Meluhha that many historians identify with the Indus region.
Unlike Egypt or Mesopotamia, the Harappan cities have yielded few obvious palaces, monumental tombs or royal inscriptions. This has led to debate over how the society was governed, whether by kings, councils, merchant elites or some other arrangement. Evidence for large-scale warfare is also thin, though that should not be overstated.
The civilization declined from around 1900 BCE, with cities shrinking and the script falling out of use. Explanations include shifting rivers, weakening monsoons and changes in trade, and most researchers favor gradual, multi-causal processes rather than a sudden catastrophe. Rediscovered in the 1920s, the Indus cities transformed understanding of South Asia's early history, showing that complex urban life there was as ancient as in the better-known river civilizations to the west.