Indus Valley Civilization

The transition of settlements from agricultural to complex urban communities, a salient feature of all late Neolithic and early Bronze Age cultures, occurred in the Indian subcontinent sometime between the early settlements at Mehrgarh and c. 3300 BC. This period marked the beginning of the earliest urban society in India, known as the Indus Valley Civilization (or, the Harappan Civilization), which thrived between 3300 BC and 1900 BC. It was centred along the Indus River and its tributaries, including the Ghaggar-Hakra River, and extended into the Ganges-Yamuna Doab, Gujarat, and northern Afghanistan.
The civilization is noted for its cities built of brick, road-side drainage system and multi-storeyed houses. The earliest historic references to India may be those to the Meluhha in Sumerian records, possibly referring to the Indus Valley civilization. When compared to the contemporary civilizations of Egypt and Sumeria, the Indus Civilization possessed unique urban planning techniques, covered the largest geographical area, and may have been a single state, as suggested by the amazing uniformity of its measurement systems.
The Mohenjo-daro ruins were once the centre of this ancient society. Indus Civilization settlements spread as far south as present-day Bombay, as far east as Delhi, as far west as the Iranian border, and as far north as the Himalayas. Among the settlements were the major urban centres of Harappa and Mohenjo-daro, as well as Dholavira, Ganweriwala, Lothal, Kalibanga and Rakhigarhi. At its peak, some archaeologists opine that the Indus Civilization may have had a population of well over five million.
To date, over 2,500 cities and settlements have been found, mainly in the general region to the east of the Indus River in Pakistan along what is claimed by many to be the Saraswati River mentioned in the Vedas. It is thought by some that geological disturbances and climate change, leading to a gradual deforesatation may ultimately have contributed to the civilization's downfall.
Archaeological resources suggest that the diverse geography of ancient India was increasing in the amount and specialization of faunal remains around 2400 to 1500 BC. This specialization suggests that the Indus Valley Civilizations were dependent upon the alluvial soils of the rivers, which produced high yield crops. By 2600 BC, the presence of a state level society is evident, complete with hierarchical rule and large scale public works. These include accomplishments such as irrigation, warehouses for grain, public streets, and brick-lined drainage systems for sanitation. Around the mid 2nd millennium BC, the region of the Indus River basin, in which approximately two-thirds of currently known sites were located dried up, and the sites were abandoned.