What is the acropolis above?

An acropolis is a hill in Greece which means "upper city". When a city-state was formed, a hill was fortified as a refuge during attack - it contained a temple of the patron god/goddess and the settlement's valuables were stored there under protection of the deity. As the area developed, a city grew up around it, often walled. The Acropolis of Athens came to have several temples, one of which is the Parthenon (parthenos = the virgin Athena, patron goddess) where the treasury was located under her protection and her statue presided.