The known world before the discovery of the Americas.
Rome is a well-known example of an ancient city that served political and commercial functions, as well as acting as a cultural and social center.
Many early cities were surrounded by patrolled walls, demonstrating the importance of protection in urban centers of early civilizations.
Early cities developed in a number of regions, from Mesopotamia to Asia to the Americas. The very first cities were founded in Mesopotamia after the Neolithic Revolution, around 7500 BCE. Mesopotamian cities included Eridu, Uruk, and Ur. Early cities also arose in the Indus Valley and ancient China. Among the early Old World cities, one of the largest was Mohenjo-daro, located in the Indus Valley (present-day Pakistan); it existed from about 2600 BCE, and had a population of 50,000 or more. In the ancient Americas, the earliest cities were built in the Andes and Mesoamerica, and flourished between the 30th century BCE and the 18th century BCE.
Ancient cities were notable for their geographical diversity, as well as their diversity in form and function. Theories that attempt to explain ancient urbanism by a single factor, such as economic benefit, fail to capture the range of variation documented by archaeologists. Excavations at early urban sites show that some cities were sparsely populated political capitals, others were trade centers, and still other cities had a primarily religious focus. Some cities had large dense populations, whereas others carried out urban activities in the realms of politics or religion without having large associated populations. Some ancient cities grew to be powerful capital cities and centers of commerce and industry, situated at the centers of growing ancient empires. Examples include Alexandria and Antioch of the Hellenistic civilization, Carthage, and ancient Rome and its eastern successor, Constantinople (later Istanbul).
The Formation of Cities
Why did cities form in the first place? There is insufficient evidence to assert what conditions gave rise to the first cities, but some theorists have speculated on what they consider pre-conditions and basic mechanisms that could explain the rise of cities. Agriculture is believed to be a pre-requisite for cities, which help preserve surplus production and create economies of scale. The conventional view holds that cities first formed after the Neolithic Revolution, with the spread of agriculture. The advent of farming encouraged hunter-gatherers to abandon nomadic lifestyles and settle near others who lived by agricultural production. Agriculture yielded more food, which made denser human populations possible, thereby supporting city development. Farming led to dense, settled populations, and food surpluses that required storage and could facilitate trade. These conditions seem to be important prerequisites for city life. Many theorists hypothesize that agriculture preceded the development of cities and led to their growth.
A good environment and strong social organization are two necessities for the formation of a successful city. A good environment includes clean water and a favorable climate for growing crops and agriculture. A strong sense of social organization helps a newly formed city work together in times of need, and it allows people to develop various functions to assist in the future development of the city (for example, farmer or merchant). Without these two common features, as well as advanced agricultural technology, a newly formed city is not likely to succeed.
Cities may have held other advantages, too. For example, cities reduced transport costs for goods, people, and ideas by bringing them all together in one spot. By reducing these transaction costs, cities contributed to worker productivity. Finally, cities likely performed the essential function of providing protection for people and the valuable things they were beginning to accumulate. Some theorists hypothesize that people may have come together to form cities as a form of protection against marauding barbarian armies.