Hamlets are predominantly agricultural areas with some sparse human settlements, while villages are small aggregates of dwellings forming communities. Towns are larger aggregates of dwellings, while cities are even larger settlements. A megalopolis is formed when when urban expansion results in an overlap in development by cities in close proximity to one another, resulting in a network of high-density human settlements.

The Feudal System, which prevailed in Europe and other parts of the world throughout the Medieval Period, significantly hindered the growth of cities. In order for Feudalism to work, a large proportion of the population has to be tied to the land in the form of serfs, or peasant farmers. This hinders urbanization because there is little surplus labor and no established middle class.

Mexico City, the largest city in Mexico and one of the most densely populated cities in the world, rests on the same site as the capital city of the Aztec Empire, called Tenochtitlan.

A surplus of food was necessary for the establishment of the world’s earliest cities. A surplus of food means that there is enough food to support population growth and, just as importantly, to support non-agricultural laborers and citizens. In order for buildings to be constructed, government to emerge, and a standing army to arise in a city a society must be able to support a proportion of the population in non-agricultural work.

During the Renaissance Era of European history, European cities experienced dramatic growth. Urbanization took place at a fast pace and colonial riches began to support a burgeoning middle class. However, throughout the rest of the world the impact of European conquest and disease led to sporadic and sometimes disastrous decline for many cities and civilizations. Cities like Tenochtitlan in modern-day Mexico and Cusco in modern-day Peru are two classic examples.

Human civilization began with the Neolithic Revolution, also called the First Agricultural Revolution, several thousand years ago. The first cities arose in close proximity to agricultural hearths like the Nile River because these regions could provide enough food to sustain a large population.

Agriculture occurred mainly in rural areas surrounding the ancient city. Agricultural producers could then bring their crops and animal products to the ancient city to sell or trade, but they would not produce within the ancient city.

Cereal grains are typically more shelf-stable than dairy and garden vegetables, and livestock can be transported closer to urban markets for slaughter. Dairy, fruits and vegetables have the potential to spoil rapidly without refrigeration, so traditionally these farmlands are just outside the urban markets.

The development of food surpluses, or more food than farmers need, allows a population of nonfarmers to exist. Those nonfarmers can specialize in the fields and conduct the services needed for the development of cities, which are fed by the farmers. After the development of agricultural surpluses, people can perform nonfarming jobs, including those related to politics, and formal political organizations can subsequently develop. Privitization of land ownership occurred before urbanization and does not influence its trajectory. And currency has been primarily an outgrowth of the social stratification that occurs as trade grows between farmers and nonfarmers.

Housing in urban centers was actually more expensive than housing in rural areas, due to the high value of land. Since cities are much more densely populated than rural areas, the competition for land is greater, driving up the cost of housing.