The following are some of the features of cities: (i) Ancient cities mostly emerged as riverine civilisations like Ur, Nippur and Mohenjodaro. (ii) Cities developed only with the increase in food supply so that it could support non-food producers. (iii) Cities were often centres of political power with administrative network, trade and industry. In medieval Europe, some towns and cities also emerged in the periphery of religious institutions like Church or important buildings. (iv) Cities were of different sizes and complexity. It could be a modern day metropolis which combined political and economic functions for an entire region or a smaller town.