semidomes

A semidome is a vault whose surface forms only half of a dome, typically created as a hemispherical or shallow arched cap that covers a semicircular or polygonal space. It may be a true hemispherical dome cut along a horizontal plane, or a curved vault that reads as a half-dome in plan and section.

In architecture, semidomes crown apses, niches, or transitional spaces between rectangular bays and circular or polygonal domed volumes. They are commonly supported by arches, squinches, or pendentives that transfer weight to the surrounding walls or piers. The shape can enhance acoustics, frame rear altars, and provide a visually elevated focal point.

Historically, semidomes are prominent in Byzantine architecture, where sequences of semidomes around the central dome reinforce the interior’s spatial rhythm, and in Islamic architecture, where half-domed surfaces appear above arches or prayer niches. They have continued to appear in later revivals and in modern curvilinear ceilings.

Decorative programs often treat semidomes as surfaces for mosaics, plasterwork, or tile, with radial or geometric patterns that emphasize the curvature and central light source.

Origin of term: derived from semi- meaning half and dome, referring to the half-dome geometry.