Domes

Dome is a particular type of vault, with a semispheric form, without angles or corners, which allows huge spaces in buildings, as well as the possibility of a powerful lighting. Despite they are thin, domes are the strongest architectural element, thanks to compressive and frictional forces the create.

Before domes, buildings were very space unefficient, as big columns were necessary to support the roof. Although the first examples of wooden spherical structures appear as soon as 6000 BC in Cyprus, they are not big enough to be considered true domes. The first big stone domes are built for tombs such as the tholos of the Treasure of Atreus (Mycenae, 13th century BC) and the Stupa in Sanchi (India, 3rd century BC). These structures are not high since they lie directly on the ground, being he dome subterraneous.

From the Pantheon to Hagia Sofia

It was the Roman civilisation the first to construct buildings with semispheric domes. Examples are known since times of Nero, achieving the culminating point with the Pantheon of Hadrianus, built in 125 AD, and still standing. Due to its huge weigth, engineers had to carve hollows inside the dome, and besides build very thick walls able to support it.

Paralelly, in Persia appeared the first domes in which pendentives were used from the beginning. This new element provided a strong support to domes, allowing them to become higher and the walls to become progressively thinner. First examplesare found in the Sassanid palaces of Firuzabad and Fars, erected around 240 and 430, respectively. The technique spread to other areas of Central Asia, being most importants the mausoleums of Bokhara (943) and Tim (978), but it did not evolve dramatically.

The idea of the pendentive arrived in Byzantium, and there it was very used and improved. The maximum achievement of this technique was Hagia Sofia in Constantinople (537), a true architectural wonder of the era, which was the largest dome in the world for almost one thousand years. The lighting provided is particularly good, thanks to the possibility it left to unload the building walls with weight, and inserting windows instead. It was also Byzantine engineers who designed the Mosque of the Rock (691) in Jerusalem and the Great Mosque of Damascus (715). Soon the Islamic style adopted the so-called onion dome, which later passed to Russia in the XIII century.

Meanwhile, in Western Europe, domes disappeared from architecture after the fall of the Roman Empire. There were several good attempts, such as half domes (apses), rib vaults or troncoconic domes such as the one in the Baptistry of Pisa, finished in 1363 (the current one is more recent, though), but the technique of the semispheric dome had disappeared.

The reinvention of the dome

Then, Brunelleschi reinvented it with much style. He built the great dome of Santa Maria del Fiore in Florence (finished in 1418), winning his design proposal among others, even if he presented his project uncomplete to avoid being copied. He took inspiration from the circular dome in the Rome Pantheon, and designed his with double shell and octogonal shape. The dome lied on a drum, instead of directly on the roof, thus avoiding scaffolds from the ground level. In this manner he built the highest dome at the time, and a true architectonic model, since it was copied in Saint Peter of Rome by Giacomo della Porta (not Michelangelo) in 1593. The later domes of Saint Paul in London (1708) and the Capitol in Washington (1850) use the same technique.

Still paralelly, in Persia, the dome of the Oljeitu Mausoleum (Soltaniyeh, 1312) was built. This was, in fact, the first double-shell dome, and was additionaly reinforced with arches between both shells, which was an architectural revolution in the Muslim world, comparable to that of Brunelleschi. It started an architectural trend that designed domes as big as the Mausoleum of Khoja Ahmed Yasavi (Kazakhstan, 1405) and the Taj Mahal (India, 1653).

One of the most characteristic elements of the Baroc architecture was the oval dome, invented by Giacomo da Vignola (chapel of Saint Andreas, Rome, 1553) and especially developed in the churches of Bernini and Borromini. This kind of dome gave a dramatic dynamism to Baroc churches. The biggest of this kind was built by Francesco Gallo in the Basilica of Vicoforte (Italia, 1773).

In modern times, one of the greatest improvements has been the invention of the geodesic dome by R. Buckminster Fuller in the 1950's. This technique, based on the utilisation of triangular elements that distribute the forces in the structure itself, allow the construction of huge domes with great stability. Currently, the biggest semispheric dome in the world is the Globe Arena in Stockholm, finished in 1989.