The "metropolis" was any city of the Greek mainland, which practically functioned as a mother-city and sent inhabitants to the new colony. In some cases there were more than one mother-cities, that could be either cities of the Greek mainland (e.g. Tanagra and Megara which founded Heraclea Pontica), or newly founded colonies (e.g. Corcyra -a colony founded by Corinth- which founded Epidamnus). Or it could be a combination of both (e.g. Corcyra -newly founded colony- and Corinth, which founded Apollonia in Illyria and Megara, Byzantium and Chalcedon, which founded Messembria on the Black Sea).

The relations between the mother-city and the colony depended each time on the moment and the existing conditions. The archaeological, mainly, finds indicate that there was a relation between a colony and its mother-city, at least in the cultural field. A characteristic example is the case of Tarentum in South Italy, which at the end of the Archaic period seems to have been influenced by its mother-city, Sparta. Moreover, the city of Dicaea -colony of Eretria in Macedonia- when it minted coins, it chose to use the same symbols with its mother-city (the cow and the octopus). On the other hand Corcyra and Syracuse, both Corinth's colonies, represent an almost exclusive example of close political relation between the mother-city and the colonies (Thucydides, Histories 1.24.1-26.2).