Muqarnas (Arabic: مقرنص‎; Persian: مقرنس‎) is a form of ornamented vaulting in Islamic architecture, the “geometric subdivision of a squinch, or cupola, or corbel, into a large number of miniature squinches, producing a sort of cellular structure”, sometimes also called a “honeycomb” vault. It is used for domes, and especially half-domes in entrances, iwans and apses, mostly in traditional Persian architecture. Where some elements project downwards, the style may be called mocárabe; these are reminiscent of stalactites, and are sometimes called “stalactite vaults”.

Muqarnas developed around the middle of the 10th century in northeastern Iran and almost simultaneously — but apparently independently — in North Africa. Examples can be found across Morocco and by extension, the Alhambra in Granada, Spain, the Abbasid Palace in Baghdad, Iraq, and the mausoleum of Sultan Qaitbay, Cairo, Egypt. Large rectangular roofs in wood with muqarnas-style decoration adorn the 12th century Cappella Palatina in Palermo, Sicily, and other important buildings in Norman Sicily. Muqarnas is also found in Armenian architecture.

History
These are decorative honeycomb elements made of painted stucco, wood, stone or brick. These elements tumble into stalactites or fill the vaults or interior domes of many Muslim buildings 1. The muqarnas originate from the duodeciman refugees in the limestone caves of the Elborz mountains of northern Iran, full of stalactites, to escape the torture of the Seljuks. It was first the Shiite mausoleums that covered themselves with stalactites, before becoming fashionable in the Islamic world. Fashion spread by the duodeciman masons, then Sufi whose convents to the reverse were protected by the Seljuk. These symbolic caves multiplied in imamzadehs. This motif echoes unconsciously to the caves of the cult of Mithra a few centuries earlier.

The first muqarnas appeared in Iran-Iraq at the end of the 11th century, under the Seljuk dynasty (1032); They spread quickly in Syria, Turkey, Egypt and Andalusia the following century. In the eleventh century, Persian literature evokes for the first time to 1077-1078 under the name of “feet of gazelle” ( Ahou Pais ).

They undoubtedly evoke the starry sky at night in the deserts, and connect their symbol to the Arab astronomers of the courts.

They also serve as elements of harmonious transition, between the upper part of a square room, and a dome that surmounts it (as in the example of the Salon of the ambassadors of the Alcazar of Seville ).

When the mocárabes come down from the corners of the room and not from the ceiling, we speak of honeycomb stalactites.

The Nasrid architecture combined the muqarnas with the arch of lambrequins to create the muqarnas arch.

Structure
Muqarnas is typically applied to the undersides of domes, pendentives, cornices, squinches, arches and vaults. Muqarnas cells are arranged in horizontal courses, as in a corbelled vault, with the horizontal joint surface having a different shape at each level. The edges of these surfaces can all be traced on a single plan view; architects can thus plan out muqarnas geometrically, as the image illustrates. See these diagrams for clarity.

Muqarnas does not have a significant structural role. Muqarnas need not be carved into the structural blocks of a corbelled vault; it can be hung from a structural roof as a purely decorative surface. Muqarnas may be made of brick, stone, stucco, or wood, and clad with tiles or plaster. The individual cells may be called alveoles.

Muqarnas is generally a downward-facing shape; that is, a vertical line can be traced from the floor to any point on a muqarnas surface. However, some muqarnas elements have been designed with upwards-facing cells.

Source From Wikipedia