Classify arches by the geometry of the intrados: the number and position of the centres (one for round and segmental, two for pointed, three or four for basket and Tudor arches), or a single continuous curve (ellipse, parabola, catenary), and distinguish true arches, with voussoirs, from corbelled “arches” of oversailing courses.
Rules · Ornament · Arches · Doors & windows
The alfiz
Frame an important arch with a rectangular moulding or band rising from its springing, so that the curved opening is set within a square field.
The alfiz turns an arch into a panel. The spandrels inside the frame are filled with carving or mosaic, and the frame itself carries an inscription or a band of pattern. The motif appears at the mihrab and the gates of Córdoba and runs through the architecture of al-Andalus and the Maghreb into Mudéjar Spain. The rectangular frame of the Persian pishtaq is a monumental relative.
Related rules
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
Carry the curve of the arch beyond the semicircle, so that the opening at the springing is narrower than its greatest width.
springing width = 2R cos β, where the arc continues β below the centre line
Alternate voussoirs of two colours (red brick and pale stone, or black and white stone) to make the structure of the arch legible as ornament.
To draw a star pattern, cover the surface with a tiling of polygons, draw two lines through the midpoint of every edge at the same angle to it, continue each line until it meets another, and erase the tiling.
pattern = tiling + contact angle θ at every edge midpoint
Keep the grid and vary the angle at which the lines cross the edges: a small angle gives broad, blunt stars; a large one gives slender, sharp stars.
Cite this page Chris Paton, “The alfiz”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/alfiz-frame. Text, drawings and models licensed under CC BY-NC 4.0.