An onion dome (Russian: луковичная глава, lúkovichnaya glava) is a dome whose shape resembles an onion, after which they are named. Such domes are often larger in diameter than the drum upon which they are set, and their height usually exceeds their width. These bulbous structures taper smoothly to a point.
It is the predominant form for church domes in Russia (Russian: луковичная глава, lúkovichnaya glava; mostly on Russian Orthodox churches) and Bavaria, Germany (German: Zwiebelturm (= "onion tower"), plural: Zwiebeltürme, mostly on Catholic churches), but can also be found regularly across Austria, Eastern Europe, Mughal India, the Middle East and Central Asia.
Other types of Orthodox cupolas are helmet domes (for example, those of the Saint Sophia Cathedral in Novgorod and Assumption Cathedral in Vladimir), Ukrainian pear domes (Saint Sophia Cathedral in Kiev), and Baroque bud domes (St. Andrew's Church in Kiev).
Art historians disagree when and why onion domes became a typical feature of Russian architecture. Byzantine churches and architecture of Kievan Rus were characterized by broader, flatter domes without a special framework erected above the drum. In contrast to this ancient form, each drum of a Russian church is surmounted by a special structure of metal or timber, which is lined with sheet iron or tiles.
By the end of the nineteenth century, most Russian churches from before the Petrine period had bulbous domes. The largest onion domes were erected in the seventeenth century in the area around Yaroslavl, incidentally famous for its large onions. Quite a few had more complicated bud-shaped domes, whose form derived from Baroque models of the late seventeenth century. Pear-shaped domes are usually associated with Ukrainian Baroque, while cone-shaped domes are typical for Orthodox churches of Transcaucasia
Traditional view 
Russian icons painted before the Mongol invasion of Rus do not feature churches with onion domes. Two highly venerated pre-Mongol churches that have been rebuilt—the Assumption Cathedral and the Cathedral of St. Demetrius in Vladimir—uniquely display golden helmet domes. Restoration work on several other ancient churches revealed some fragments of former helmet-like domes below newer onion cupolas.
It has been posited that onion domes first appeared during the reign of Ivan the Terrible. The domes of Saint Basil's Cathedral have not been altered since the reign of Ivan's son Fyodor I, indicating the presence of onion domes in the sixteenth-century Russia.
Some scholars postulate that onion domes were borrowed by Russians from Muslim countries - probably from the Khanate of Kazan, whose conquest Ivan the Terrible commemorated by erecting St. Basil's Cathedral. Some believe that onion domes first appeared in Russian wooden architecture above tent-like churches. According to this theory, onion domes were strictly utilitarian, as they prevented snow from piling on the roof.
Based on the notion that onion domes did not exist in Russia before the mid-sixteenth century, restoration work on churches built before the seventeenth century have routinely involved replacement of onion domes with "more authentic" helmet-shaped domes. One example of such restoration is the Dormition Cathedral in the Moscow Kremlin.
Modern view 
In 1946, the historian Boris Rybakov, while analysing miniatures of ancient Russian chronicles, pointed out that most of them, from the thirteenth century onward, display churches with onion domes rather than helmet domes. Nikolay Voronin, the foremost authority on pre-Mongol Russian architecture, seconded his opinion that onion domes existed in Russia as early as the thirteenth century, although they presumably could not be widespread. These findings demonstrated that Russian onion domes could not be imported from the Orient, where onion domes did not replace spherical domes until the fifteenth century.
Sergey Zagraevsky, a modern art historian, surveyed hundreds of Russian icons and miniatures, from the eleventh century onward. He concluded that most icons painted after the Mongol invasion of Rus display only onion domes. First onion domes displayed on some pictures of twelfth century (two miniatures from Dobrylov Evangelie).  He found only one icon from the late fifteenth century displaying a dome resembling the helmet instead of an onion. His findings led him to dismiss fragments of helmet domes discovered by restorators beneath modern onion domes as post-Petrine stylisations intended to reproduce the familiar forms of Byzantine cupolas. Zagraevsky also indicated that the oldest depictions of the two Vladimir cathedrals represent them as having onion domes, prior to their replacement by classicizing helmet domes.
Zagraevsky explains the ubiquitous appearance of onion domes in the late thirteenth century by the general emphasis on verticality characteristic of Russian architecture from the late twelfth to early fifteenth centuries. At that period, porches, pilasters, vaults and drums were arranged to create a vertical thrust, to make the church seem taller than it was. It seems logical that elongated, or onion, domes were part of the same proto-Gothic trend aimed at achieving pyramidal, vertical emphasis.
Prior to the eighteenth century, the Russian Orthodox Church did not assign any particular symbolism to the exterior shape of a church. Nevertheless, onion domes are popularly believed to symbolise burning candles. In 1917, noted religious philosopher Prince Yevgeny Trubetskoy argued that the onion shape of Russian church domes may not be explained rationally. According to Trubetskoy, drums crowned by tapering domes were deliberately scored to resemble candles, thus manifesting a certain aesthetic and religious attitude. Another explanation has it that the onion dome was originally regarded as a form reminiscent of the edicula (cubiculum) in the Church of the Holy Sepulchre in Jerusalem.
Onion domes often appear in groups of three, representing the Holy Trinity, or five, representing Jesus Christ and the Four Evangelists. Domes standing alone represent Jesus. Vasily Tatischev, the first to record such interpretation, disapproved of it emphatically. He believed that the five-domed design of churches was propagated by Patriarch Nikon, who liked to compare the central and highest dome with himself and four lateral domes with four other patriarchs of the Orthodox world. There is no other evidence that Nikon ever held such a view.
The domes are often brightly painted: their colors may informally symbolise different aspects of religion. Green, blue, and gold domes are sometimes held to represent the Holy Trinity, the Holy Spirit, and Jesus, respectively. Black ball-shaped domes were once popular in the snowy north of Russia.
Outside Russia 
The onion dome is not only found in Russian Architecture: it was also used extensively in Mughal architecture, which later went on to influence Indo-Gothic architecture. Outside India, it is also used in Iran and other places in the Middle East and Central Asia.
Baroque domes in the shape of an onion (or other vegetables or flower-buds) were common in the Holy Roman Empire as well. The first one was built in 1576 by the architect Hans Holl (1512-1594) on the church of Saint Mary Star Abbey in Augsburg. Usually made of copper sheet, onion domes appear on Catholic churches all over southern Germany, Czech lands, Austria and Northeast Italy. Onion domes were also a favourite of 20th-century Austrian architectural designer Friedensreich Hundertwasser.
See also 
Notes and references 
- Compare the iconic domes of the Taj Mahal built in 1630.
- A.П.Новицкий. Луковичная форма глав русских церквей. В кн.: Московское археологическое общество. Труды комиссии по сохранению древних памятников. Т. III. Moscow, 1909.
- Б.А.Рыбаков. «Окна в исчезнувший мир (по поводу книги А.В.Арциховского «Древнерусские миниатюры как исторический источник»). В кн.: Доклады и сообщения историч. факультета МГУ. Вып. IV. М., 1946. С. 50.
- Н.Н.Воронин. Архитектурный памятник как исторический источник (заметки к постановке вопроса). В кн.: Советская археология. Вып. XIX. М., 1954. С. 73.
- S. V. Zagraevsky. Forms of the domes of the ancient Russian temples. Published in Russian: Заграевский С.В. Формы глав (купольных покрытий) древнерусских храмов. М.: Алев-В, 2008.
- Г.К.Вагнер. О своеобразии стилеобразования в архитектуре Древней Руси (возвращение к проблеме). В кн.: Архитектурное наследство. Вып. 38. М., 1995. С. 25.
- See, for instance, the most authoritative survey of early Russian architecture: П.А.Раппопорт. Древнерусская архитектура. СПб, 1993.
- Another important consideration proposed by Zagraevsky links the onion-shaped form of Russian domes with the weight of traditional Russian crosses, which are much larger and more elaborate than those used in Byzantium and Kievan Rus. Such ponderous crosses would have fallen aground during a storm, if they had not been fixed to sizeable stones traditionally placed inside the elongated domes of Russian churches. It is impossible to place such a stone inside the flat dome of the Byzantine type.
- Бусева-Давыдова И.Л. Символика архитектуры по древнерусским письменным источникам XI-XVII вв. // Герменевтика древнерусской литературы. XVI - начало XVIII вв. Moscow, 1989.
- "The Byzantine cupola above the church represents the vault of heaven above the earth. On the other hand, the Gothic spire expresses unbridled vertical thrust, which rises huge masses of stone to the sky. In contrast to these, our native onion dome may be likened to a tongue of fire, crowned by a cross and tapering towards a cross. When we look at the Ivan the Great Bell Tower, we seem to see a gigantic candle burning above Moscow. The Kremlin cathedrals and churches, with their multiple domes, look like huge chandeliers. The onion shape results from the idea of prayer as a soul burning towards heaven, which connects the earthly world with the treasures of the afterlife. Every attempt to explain the onion shape of our church domes by utilitarian considerations (for instance, the need to preclude snow from piling on the roof) fails to account for the most essential point, that of aesthetic significance of onion domes for our religion. Indeed, there are numerous other ways to achieve the same utilitarian result, e.g., spires, steeples, cones. Why, of all these shapes, ancient Russian architecture settled upon the onion dome? Because the aesthetic impression produced by the onion dome matched a certain religious attitude. The meaning of this religious and aesthetic feeling is finely expressed by a folk saying - "glowing with fervour" - when they speak about church domes". - See Е.Н.Трубецкой. Три очерка о русской иконе. 1917. Новосибирск, 1991. С. 10.
- Лидов А.М. Иерусалимский кувуклий. О происхождении луковичных глав. // Иконография архитектуры. Moscow, 1990.
- Media related to Onion domes at Wikimedia Commons