Occupation at the acropolis dates back to prehistoric times. A Mycenaean palace sat here in the Late Bronze Age and it served as a political and religious center in the Archaic period. The acropolis was dedicated to religious functions only in Classical times. Following the Classical period, this area was always a key military position, the first part of the city taken during invasions (e.g., by the Franks, Venetians, Turks, Bavarians).
Read more at http://www.bibleplaces.com/athensacropolis.htm