A polis (pl. poleis) is a city, or a city-state. The word originates from the ancient Greek city-states, which developed in the Hellenic period and survived with decreasing influence well into Roman times.
The territory of the ancient polis were centered around a citadel, called the acropolis. There would of necessity also be an agora (market) and a gymnasion. Most people lived in the countryside, but with only a short travel to the civic center. The Greeks did not regard the polis as a territorial unit so much as a religious and political association. Each city was composed of several tribes or demes, which were in turn composed of phratries and finally gentes. Metics (resident foreigners) and slaves lay outside this organization. Citizenship was typically determined by birth. Each polis also had a number of protecting gods and its own particular festivals and customs.
See also: synoecism, apoikia