Usually cities grow up around administrative, commercial and religious centers or places of popular pilgrimage. Growth of cities mainly depends on the surplus food production of the neighboring villages. Cities cannot exist if the people residing in the hinterland of cities fail to develop any food producing economy on a large scale.
In Ancient India, urbanization and emergence of towns and cities took off around 2350 B.C when apart from big cities like Mohenjodaro, Harappa, Lothal and Kalibangan, smaller cities too took shape.
After the decline of Harappan civilisation approximately in 1500 B.C. the urban trend in India ceased to exist for a long time.
In the pastoral Rig-Vedic society (1500-1000 B.C), there was no question of agricultural surplus. For this reason trade and commerce could not flourish, and the rural economy of the Rig-Vedic period could not transform into urban economy.
A permanent and stable agrarian economy developed in the Later-Vedic era (1000-600 B.C). The Aryans began to colonize in the central Gangetic plains. Farming advanced with the use of iron tools in fertile soil, and surplus agricultural products led to various vocations. Trade flourished and cities started emerging in the Gangetic plains around 6th century B.C. — nearly a thousand years since the urban Harappan culture was wiped out. This phase is called the Second Urbanization. Kaushambi, Kosal, Vidarbha, Ahichhatra and Hastinapur are noted cities — mainly political strongholds — in the Later-Vedic era.
India, around the time of Buddha, had sixty cities, the principal ones being Champa, Rajagriha, Sravasti, Saket, Kaushambi, Varanasi, Vaisahali and Chirand. Vocational crafts had led to their rise. Later, urbanization grew in the Maurya and post-Maury ages.