thumb|350px|The Acropolis of Athensthumb|250px|A view of Athens from the AcropolisAcropolis (Gr. akros, akron, edge, extremity + polis, city, pl. acropoleis) literally means edge of the city. In Greek, Acropolis means "Highest City". For purposes of defense, early settlers naturally chose elevated ground, frequently a hill with precipitous sides. In many parts of the world, these early citadels became the nuclei of large cities, which grew up on the surrounding lower ground, such as modern Rome.

The word Acropolis, although Greek in origin and associated primarily with the Greek cities Athens, Argos, Thebes, and Corinth (with its Acrocorinth), may be applied generically to all such citadels, including Rome, Jerusalem, Celtic Bratislava, many in Asia Minor, or even Castle Rock in Edinburgh.

The most famous example is the Acropolis of Athens, which, by reason of its historical associations and the several famous buildings erected upon it (most notably the Parthenon), is known without qualification as the Acropolis. Although originating in the mainland of Greece, use of the acropolis model quickly spread to Greek colonies such as the Dorian Lato on Crete during the Archaic Period.

Because of its classical Greco-Roman style, the ruins of Mission San Juan Capistrano's Great Stone Church in California, United States has been called the "American Acropolis".

Other parts of the world developed other names for the high citadel or alcázar, which often reinforced a naturally strong site. In Central Italy, many small rural communes still cluster at the base of a fortified habitation known as La Rocca of the commune.

The term acropolis is also used to describe the central complex of overlapping structures, such as plazas and pyramids, in many Mayan cities, including Tikal and Copán.