Revisiting the Geometry of the Transition Zone Using Filposh Squinches in Ardeshir Palace

Iranians invented squinches to cover a square-plan space with a dome. Filposh, a type of squinch first found in Sasanian architecture, is a conical vault constructed in the transition zone’s corners to transmit the dome’s forces and weight. This technique can be seen in three halls of the Sasanian palace of Ardeshir. In this paper, the geometry of the transition zone using filposh squinches between a spherical dome and the square supporting walls in Ardeshir Palace was re-examined. A historical descriptive method was employed to analyse the main drawings of the halls from the nineteenth century to the present, and two hypotheses concerning the geometry of the transition zone were modelled and evaluated. As a result, the hypothesis that the dome’s cross-section intersects the chamber’s square plan is rejected. Furthermore, the claim that the transition zone’s square plan circumscribes the dome’s cross-section was discussed and proven.