Cities are large settlements with many people, buildings, and organized systems. They include roads, markets, and places for government or trade. Cities have existed for thousands of years.

Ancient cities such as Ur in Mesopotamia had walls, temples, and busy streets. Modern cities include transportation systems, schools, and large populations. Cities are found in both ancient and present-day societies.

Cities are studied in history and geography. Evidence includes building remains, infrastructure, and records of population and trade.