The structure is Doric in style, but there are Ionic columns in the interior of the central building. Both east and west façades of the central building have six columns, but the distance between the central columns of each façade is half again as wide as the other intercolumniations. This permitted the central passageway to be wider and required an extra triglyph and metope in the frieze.
The central building consists of two porches sitting at two levels, lower on the west and higher (both at the floor level and at the roof) on the east. The west porch is much deeper than the east porch, providing the aforementioned waiting area outside the gate wall. At the top of the five-step ascent to the upper, east porch was the cross wall that regulated entrance to the Acropolis. Five doors pierced the wall, one for each of the intercolumniations of the façade. The center door was wider than the others, and, of the two doors on each side, the one closer to the building's longitudinal axis was wider.
The construction of the building seems to have been roughly from the northwest toward the southeast. The west façade, where all three parts of the building present themselves, gains cohesion from the platform on which all three parts rest. That platform consists of four steps, but the lowest of the four is, on the sides only, constructed of darker Eleusinian stone so that the height of the base there is visually reduced, reflecting the fact that the columns and the entire wing structures are shorter by roughly the same proportion.
The platform is split by the central passageway leading into the Acropolis. Though the passage is now covered by a wooden ramp for tourists, the original passage provided a route into the Acropolis without steps.
The platform does not show curvature, but the entablature of the central building does.
The central building had a pediment facing west and another facing east, though intended pedimental sculpture was never installed.
The west wings had hipped roofs on three sides; the fourth side abutted the walls separating the western wings from the never-constructed east wings.
The central building had a ceiling of marble coffer blocks, painted and having gilded stars.
