The Indus civilization flourished for half a millennium from about 2600 bc to 1900 bc. Then it mysteriously declined and vanished from view. It remained invisible for almost 4,000 years until its ruins were discovered by accident in the 1920s by British and Indian archaeologists. Following almost a century of excavation, it is today regarded as a civilization worthy of comparison with those of ancient Egypt and Mesopotamia, as the beginning of Indian civilization and possibly as the origin of Hinduism.
More than a thousand Indus settlements covered at least 800,000 square kilometres of what is now Pakistan and northwestern India. It was the most extensive urban culture of its period, with a population of perhaps 1 million and a vigorous maritime export trade to the Gulf and cities such as Ur in Mesopotamia, where objects inscribed with Indus signs have been discovered. Astonishingly, the culture has left no archaeological evidence of armies or warfare.
Most Indus settlements were villages; some were towns, and at least five were substantial cities. The two largest, Mohenjo-daro — a World Heritage Site listed by the United Nations — located near the Indus river, and Harappa, by one of the tributaries, boasted street planning and house drainage worthy of the twentieth century ad. They hosted the world's first known toilets, along with complex stone weights, elaborately drilled gemstone necklaces and exquisitely carved seal stones featuring one of the world's stubbornly undeciphered scripts.