An acropolis is the high point of a Greek city. The best known is this, the Acropolis of Athens.

The Parthenon is the most famous building on the Acropolis. Building of temple monuments on the acropolis began in the 6th century B.C. In 480, when the Persians ravaged Athens [see Battle of Thermopylae], it provided a clean slate for Periclean building projects on the acropolis.

Aristophanes used the term "acropolis" to refer to Athens.

The acropolis could also be referred to simply as polis.

"The normal fifth-century Attic term for the Acropolis was polis, as Thucydides informs us, and Kallias' usage represents the earliest certain epigraphic exception. The next occurrence is firmly dated 410/09 B.C. The first Athenian author known to employ akropolis for Athens is Aristophanes and he does not do this until the Lysistrata (spring 411 B.C.).27 Now in most extant examples of polis meaning 'Acropolis' the noun is coupled with a local preposition without the article."
~"Two Notes on Athenian Financial Document," by Harold B. Mattingly; The Annual of the British School at Athens, (1967), pp. 13-17

Glossary entry on Acropolis