Metropolis or metropolis[1]​ is the term used in Ancient Greece for the cities from which a colony would later be created. The metropolises had a decisive political influence in the colonies and were also the religious, economic, cultural and social centers of the region. From the time of the Roman Empire, some important cities were renamed metropolises. The use of the term in the century is not clearly delimited. Global cities are usually determined this way. Unlike a global city, which has international importance, a metropolis can have relative importance in a certain region, e.g. artistic or financial metropolis. The increasing concentration of economy, administration and culture is known as metropolization. In dependency theory, the opposite of the periphery is called a metropolis. According to some definitions, the population of a metropolis would vary between 1 and 10 million people. From 10 million onwards, the term “megacity”, “megalopolis” or “megalopolis” is used. In metropolises that stand out for their economic importance, the number of inhabitants plays a key role.

Metropolis is a Greek word, which comes from μήτηρ, mḗtēr meaning "mother" and πόλις, pólis meaning "city", which is how the ancient Greek colonies referred to their original cities, with which the cult and political-cultural connections were preserved. The word was used in postclassical Latin for the principal city of a province, the seat of government, and in particular ecclesiastically for the seat of a metropolitan bishop to whom the suffragan bishops were responsible. This use equates the province with the diocese or episcopal see.

The metropolis provides its inhabitants with all the services, unlike what happens in other types of urban centers (such as a neighborhood, village, town). At the same time, the economic activities that are carried out here are in great quantity and there is a higher level of complexity in them. The formation of metropolises is one of the most studied urban topics because it is in these urban settlements where all kinds of problems arise that are generally shared between these large cities. Among the problems that characterize metropolises we can highlight:[2]​.