Also on the Acropolis, built after the Parthenon between 421 and 406 BC, the Erechtheion stands at the sacred site of where Poseidon left his triden marks in a rock and Athena's tree sprouted. This is the front of the monument.
It is most famous for its elegant Porch of the Caryatids. These columns in the shape of maidens are copies; the originals are indoors at the new Acropolis Museum.
Here is a detail of the ceiling of the Erechtheion.