The Erechtheion occupies a sloping site on the Akropolis, where an older temple, destroyed by Persians, once had stood. Spoils of the Persian comquest were preserved in it with other relics, held in special veneration.

The nucleus of the design is a cella, inner room, without colonades, the sanctuary of Athena Polias, the City's Guardian, Erechthonius, a mythic hero of the Athenians, and Poseidon, the ocean-god.

The exterior is distinguished by two Ionic porticoes and by the third, the southern, in which the columns are replaced by six draped female figures whose heads support a heavy architrave of pentelic marble. They were called Caryatids because the models for them were women from Caryai, in Lakonia. All these figures face south, the three to the west, resting their weight on the right legs, the three eastern on the left, giving to the contour of their bodies the effect of entasis, a slight convexity correction.

The Erechtheion project was postponed after the outbreak of the Peloponnesian Wars, in 432 BC, the works started in 421 BC and have been completed in 406 BC.