A polis (πόλις) — plural: poleis (πόλεις) — is a city, or a city-state. The word originates from the Greek city-states, which developed during the Hellenic period and survived (though with decreasing influence) well into Roman times.
The territory of an ancient polis centred around a citadel, called the acropolis, and would of necessity also have an agora (market) and a gymnasion. Most people lived in the countryside, but only a short journey away from the civic centre. 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. Birth typically determined citizenship. Each polis also had a number of protecting gods and its own particular festivals and customs.
Derivatives of polis are common in many modern European languages. This is indicative of the influence of the polis-centred Hellenic world view. Derivative words in English include policy, police and politics.