Rules · Cities · Walls · Structure
Defend the circle in depth: a moat, an outer wall, an open space between the walls, and a massive main wall with towers; bring each road in through a gate that turns, and set a domed chamber over the main gate from which the country can be watched.
Al-Khatib’s authorities describe a water-filled moat, an outer wall, an intervallum (fasil), and a main wall of sun-dried brick much thicker at its base than its top, with some twenty-eight towers between each pair of gates; a third, lighter wall separated the houses from the central court. The entrances passed through the outer and main walls by vaulted passages that forced a turn (the bent entrance long used in Near Eastern fortification), and above each gate of the main wall was an audience chamber under a dome.
Such a triple ring was more than any threat of the time required, and its purpose was partly symbolic: it enclosed the dynasty, its army and its administration, and kept the ordinary life of the city at a distance.
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
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
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
Lay out the capital as a circle with four gates at equal intervals, each facing the region its road leads to, and put the ruler’s palace at the centre, so that no part of the city is further from him than any other.
4 gates on the diagonals (Khurasan NE, Basra SE, Kufa SW, Syria NW); palace at the centre
Leave the centre of the city open: set the palace and the congregational mosque side by side in a great court, and allow round its edge only the guard, the police and the offices of state: no private houses and no markets.
palace 400 × 400 cubits; mosque 200 × 200 cubits; Green Dome 80 cubits high
Keep trade out of the ruler’s city: move the markets to a suburb outside the walls and give each trade its own street or row, with the noisome trades at the far end.
Cite this page Chris Paton, “Moat, two walls and bent gates”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/baghdad-walls-gates. Text, drawings and models licensed under CC BY-NC 4.0.