Rules · Plans · Modules · Structure
Make the prayer hall of identical bays of columns and arcades, so that it can be enlarged by adding aisles or bays without changing its character.
hall = n aisles × m bays of one module
The hypostyle hall has no single centre and no fixed size. Abd al-Rahman I’s mosque at Córdoba had eleven aisles running towards the qibla; Abd al-Rahman II lengthened them, al-Hakam II lengthened them again and added the domed bays before a new mihrab, and al-Mansur widened the whole hall by eight aisles on the east. Each campaign simply repeated the bay, which is why the building could double and double again and still read as one room, a forest of some eight hundred columns at its greatest extent.
The price of this openness is a lack of hierarchy, which later builders recovered by widening the central aisle, marking the aisle before the mihrab with domes, or, as at Kairouan, running a transverse aisle along the qibla wall to form a T.
Throw an arch diagonally across each upper corner of the square, backed by a small conch or cone; the four squinches and the four walls between them make an octagon, on which a round dome can sit.
octagon side = S (√2 − 1) ≈ 0.414 S; squinch span = octagon side
Orient the prayer hall so that its principal wall, the qibla wall, stands square to the direction of Mecca, and mark the middle of that wall with a niche, the mihrab.
qibla wall ⟂ direction of the Kaaba; mihrab on the axis
Build the congregational mosque as an enclosed courtyard (sahn) with a covered prayer hall (haram) on its qibla side and shaded porticoes (riwaq) on the others.
Where the available columns are too short for the height you want, stand a pier on each column and carry the roof on a second, upper tier of arches, bracing the piers with a lower tier of horseshoe arches.
height ≈ column + pier + upper arch; lower arch = brace
Choose the symmetry of the principal star (six-, eight-, ten- or twelve-fold) and build the field from a repeat unit that tiles the plane; stars that cannot tile by themselves are completed by secondary shapes in the gaps.
Fill a half-dome, squinch or cornice with tiers of small concave cells, each tier corbelled forward from the one below and each cell set over the junction of two cells beneath.
height = tiers × module; each tier projects inward
Cite this page Chris Paton, “The hypostyle grows by addition”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/hypostyle-additive. Text, drawings and models licensed under CC BY-NC 4.0.