They were used as structural supports for arcades, colonnades, and as pillars in semi-basements to support vaults. For arcades, stone was always used to achieve the slender proportions required and they were either square or circular in section. Stone columns were crowned with simple capitals.
In contrast, wooden columns were used for colonnades or tarmas, and came with circular or octagonal sections and often crowned by very elaborate muqarnased capitals. These capitals resemble closely the ones found in traditional houses of Baghdad and elsewhere in southern Iraq.