There were two wings planned for the east side of the Propylaea, facing in toward the Acropolis. Preparations for both wings are apparent at the eastern end of the central building and along the side walls, but it seems that the plan for a southern wing was abandoned early in the construction process since the old fortification wall was not demolished, as required for that wing.
The north wing was not built either. Had it been constructed, it seems that the level of the floor would have been problematic. To the extent that preparations had been made, they were for a floor at the level of the western portion of the building, considerably below the level required on the East.
To the right of the Propylaea and further west, on the raised bastion prepared for it, stood the Temple of Athena Nike. As a result of the outbreak of the Peloponnesian War between Athens and Sparta in 431 BC, the Propylaea was never completed. Not only are the eastern wings missing, the wall surfaces were not trimmed to their finished shapes, and so-called lifting bosses remain on many blocks. (Lifting bosses have long been called such but are now recognized to have been for another purpose, though that other purpose is not agreed. See A. Trevor Hodge, "Bosses Reappraised," Omni Pede Stare: Saggi Architettonici e circumvesuviani in memoriuam Jos de Waele, Mols & Moormann, eds.)