Typology and Distribution of Squinches in the Transition Zones of Seljuk Square Chambers in Iran

The construction of domes on square-plan chambers in Iranian architecture can be traced back to the pre-Islamic era. In order to address the challenge of building a dome with a circular cross-section on a square space, a transition zone was created using four squinches, with the objective of altering the geometry of the cross-section and making it closer to a circular shape. During the Great Seljuk era, the construction of domes on square-plan spaces became a common practice, with various squinch techniques employed in the transition zones. This paper examines forty-one existing Seljuk chambers in Iran and classifies the squinches in their transition zones into four types: predominantly shouldered arches, Patkaneh, Patkin, and Sekonj. Shouldered arches are principally observed in the transition zones of structures situated in the north-western and northeastern regions, with a few instances noted in the northern and central parts of the country. The majority of Patkaneh squinches are located in the central region of Iran. Four cases with distinct geometric solutions in the transition zones are situated in north-west Iran, and one example is located in north-east Iran. Additionally, three instances of the Patkin squinch can be observed in a caravanserai located in the north-eastern region. In the northern region, two chambers were identified in two caravanserais with Sekonj squinches in transitional zones. The use of these different squinch techniques reflects the regional preferences in architectural styles and the adaptability of Seljuk builders to local materials and construction methods. This study contributes to the scientific understanding of Iranian architectural history by classifying the squinch techniques used in Seljuk domed chambers. The analysis of forty-one structures provides insights into regional construction practices, geometric innovations, and the evolution of transition methods. The proposed typology enriches architectural historiography and provides a foundation for further comparative studies on structural solutions in Islamic and pre-Islamic architecture.