The Apadana is a hypostyle hall solved by the opposite logic to Karnak's. In Egypt the stone roof forces the columns close together; at Persepolis the roof is borne not by stone but by timber (cedar and cypress beams). Because timber resists bending far better than stone, the spacing between columns grows and the columns can become slender and tall.

The result is the signature of Achaemenid architecture: extremely slender stone-shafted columns reaching about 20 metres. That slenderness is permitted not by the stone but by the light timber roof above. The capitals end in addorsed (back-to-back) bull — or lion, griffin — protomes; this double-animal capital both carries and symbolises the cradle on which the wooden beams rest. The Apadana is thus an architectural expression of empire: materials and forms drawn from many peoples (the Egyptian cavetto cornice, Ionian stone craft, the Mesopotamian terrace tradition, the Medo-Persian column) united in a single ceremonial space.

The hall is laid out on a square plan ringed on three sides by columned porticoes, at a scale able to receive thousands; the reliefs on the eastern and northern stairways show delegations bringing gifts from every corner of the empire. Persepolis builds a wide-spanning collective interior through a hybrid stone-and-timber system — one of the most elegant post-and-lintel solutions of the ancient world.