Onion Dome

An onion dome is a dome whose profile swells out beyond the diameter of its supporting drum and then tapers to a point, like an onion bulb. It is the defining roof form of Russian Orthodox church architecture and is also widespread on Baroque churches in Bavaria, Austria and neighbouring regions.

Origins

The origin of the shape is debated. Some historians trace it to Syria and the Islamic world, with early prototypes in 11th-century Iran, and suggest Russian builders may have adopted it through contact with Muslim states such as the Khanate of Kazan. Onion domes appear on Russian buildings as early as the 13th century and were most popular in the 17th and 18th centuries. The domes of St Basil's Cathedral in Moscow, built to commemorate the conquest of Kazan in 1552, have remained unchanged since the reign of Fyodor I (1584-1598).

Construction and coverings

The onion dome is usually not a structural masonry dome but a light outer shell. In Russia, each drum is topped by a metal or timber framework clad in sheet iron or tiles. In central Europe the domes are typically clad in copper sheet, which weathers to green.

Wooden churches in northern Russia used timber shingles. The Church of the Transfiguration at Kizhi Pogost on Lake Onega, begun in 1714 and about 37 m (121 ft) tall, carries 22 domes covered in aspen shingles, using roughly 60,000 shingles held by about 180,000 nails. Kizhi Pogost is a UNESCO World Heritage site.

Snow and weather

It is sometimes said that the onion shape sheds snow better than a hemispherical dome in severe winters. Some scholars accept this as a practical advantage; others, such as Prince Evgenii Trubetskoy, argued the shape is primarily symbolic and aesthetic.

In central Europe

The first Baroque onion dome in the Holy Roman Empire is recorded in Augsburg in 1576. Onion domes now crown many village churches across Bavaria, Austria and the Alps, usually as copper-clad timber structures on church towers.

Maintenance

Copper and sheet-iron domes need periodic re-cladding and gilding, while shingled domes need replacement of weathered shingles. Restoration of Kizhi from 1999 onward involved dismantling, recording and reassembling the church and replacing elements that had decayed.