Traditional Persian Karbandi Interlacing Ribbed Squinch Vaults: Complete Master Architect Handbook

In Iranian architecture, spanning wide interior spaces without timber trusses was a structural necessity in the arid, wood-scarce plateau. From the Seljuk and Ilkhanid eras through the Safavid and Qajar dynasties, master architects (Ostads) elevated brick vaulting into both an engineering feat and a spiritual expression of celestial geometry.

Karbandi represents the pinnacle of this tradition. While a simple squinch (goosheh-sazi) merely bridges a corner, Karbandi weaves an integrated space-frame of intersecting masonry arches. This network decomposes complex spherical geometry into a harmonious array of triangular and diamond-shaped concave infill facets (shaprak and simi), crowned by a central oculus or skylight lantern (hourno).

The layout of Karbandi is determined using pure Euclidean compass-and-straightedge drafting (Hendeseh). The base chamber plan is circumscribed by a primary reference circle, which is divided into an even number of equal segments—most commonly 12, 16, or 24 points known as Pa-kar (the foot of the arch on the wall perimeter).

From each Pa-kar, a semicircular or pointed arch rib (tooyzeh) springs upward, bypassing the center and terminating at a diametrically opposite Pa-kar point. As these ribs cross each other in three dimensions, their points of intersection form secondary load-bearing nodes (Sar-kar). The resulting overhead projection forms a breathtaking dynamic star polygon (shamsi) that naturally leaves an open octagonal or polygonal ring at the apex.

The construction of Karbandi vaults is historically remarkable because it was executed largely without wooden formwork or centering (which was impossible given timber scarcity). Masons lay flat kiln-fired clay bricks (200mm × 200mm × 35mm) edge-to-edge in rapid succession.

This is made possible by Gach-e Zendeh (quick-setting gypsum plaster). Burned from local gypsum deposits, this mortar begins hydrating and sets solidly within 3 to 5 minutes of mixing. A mason holds a brick in place with one hand against the growing arch curve, applies a dab of warm gypsum paste, and within 90 seconds the bond is strong enough to support the next cantilevered brick, allowing arches to leap across open space purely through fast chemical crystallization.

Once the primary load-bearing brick rib skeleton is established, the interstitial triangular voids (shaprak) are closed using lightweight infill webbing known as Rasmi-bandi. These panels can be filled with hollow terracotta pots (tanbousheh) to reduce vault deadweight, or surfaced with stepped plaster stalactites (muqarnas).

In public bazaars, hammams, and royal caravanserais, the underside is adorned with polychrome glazed mosaic tiles (mo’arraq) or seven-color haft-rangi tiles. Historic conservation requires monitoring seismic cracking along arch rib groins and repointing with flexible lime-gypsum grouts to prevent catastrophic shear collapse during earthquakes.