As displayed in the early 20th century. Parthenon Ionic frieze in mid background, Ionic frieze from temple of Apollo Epikourios at Bassai in top background.

The third great 5th-century BCE marble building on the Acropolis is known as the Erechtheion, though this name (Erechtheos was a mythical king of Athens) has been challenged. Since the Parthenon stands immediately to the south, the architect of the Erechtheion did not attempt to make the building compete directly with this outstanding example of the Doric order, and instead chose the more ornate and delicate Ionic order. The building has an unusually complex plan. Its steeply sloping site also created drastic variations in building levels. It is famous for the smaller prostyle porch with six caryatids added to the west end of its south side--the "Porch of the Maidens."