A temple of Athena Polias (of the city), the Erechtheion (Ἐρέχθειον) was a fine example of Athenian polytheism. It begun as a building for a hero cult of Erechtheus and king Cecrops, both thought of as factual men who had lived and were instrumental to the city, thus worshipped. Eventually, it was taken over by cults of Athena of the City, Poseidon, Zeus, Hermes, and a long list of etcs.
Alongside the Erechtheion laid the Parthenon, a treasury to Athena of the City and guarded by another Athena, this one named Parthenos (the virgin). These two Athenas were guarded, in essence, by a third, Promachos (of war) which stood just feet from the entrance to the Acropolis.
The Erechtheion was, in effect, the actual temple of the most important Athena to the city, yet only a part of the cults taking place at the Acropolis.