Main dome

The main dome is the largest and highest dome in a building with several domes. In a mosque it defines the centre of the prayer hall; in a church, the central space. It shapes both the interior and the skyline, and semi-domes, smaller domes and arches step down around it.

Its place in the structure

The weight of the main dome comes down first into a drum or directly into the transition elements: pendentives, squinches or Turkish triangles. From there it passes into the great arches and the large piers they rest on. The outward thrust at the dome base is taken by semi-domes, buttresses and weight towers. Every element around a main dome is really part of a system for controlling that thrust.

The main dome in Turkish architecture

Ottoman mosque design can be read through the different ways of supporting the main dome. At the Süleymaniye, the main dome is backed by two semi-domes on the qibla axis, a layout that recalls Hagia Sophia. At the Selimiye, the main dome rests on an octagonal system of eight piers, and the interior is unified under a single great dome. The two are often compared as different answers to the same problem. We touch on that history in our piece on art and architecture through history.

Survey and 3D modeling

The real profile of a main dome rarely matches a perfect hemisphere; flattening and cracking over time only show up in measurement. Meridian sections taken from laser scan data describe the inner and outer surfaces separately. Building the dome as a surface of revolution in 3D and comparing it with the scan makes any deformation visible.