How many domes can you think of? Apart from the Millennium Dome in Greenwich, domes have a long and spectacular history. St Paul's Cathedral, the Dome of the Rock in Jerusalem, the Taj Mahal, St Peter's in Rome and the Capitol building in Washington all spring to mind. One of the newest is the dazzling metal and glass dome that protects the entrance to Canary Wharf Underground station (shown on pages 10 and 11). But for the first domes, we have to go a lot further back.
Some 6,000 years ago, unknown builders began a circular structure. As they placed circles of stones, one upon another, they began to reduce the circumference of the rings and close the gap in the roof. The finished building had the shape of an old-fashioned beehive. The weight pushed the walls outward, but heavy stones around the base prevented its collapse.
These prehistoric architects had constructed a dome - a shape that contained a large space using relatively little material. Domes have been used by builders ever since for the same mathematical reason. Because a sphere contains the largest volume in relation to surface area of any three-dimensional shape, so a dome, which is part of a sphere, uses the least roofing material to cover the largest space. (A flat roof uses less material, but would not provide the height; a pitched roof gives height, but uses more material.) Many cultures seem to have discovered the technique independently - igloos are perhaps the most familiar domes of all. Romans, Christians and Muslims used domes as symbols of power, both spiritual and secular (see over page). Ancient builders in South America, however, never discovered how to build domes or arches.
Domes have been made from many different materials. Sir Christopher Wren's St Paul's Cathedral has an outer dome of timber covered with lead. The US Capitol building in Washington DC (completed in 1863) has a cast-iron dome that is 27m across. The Palazetto dello Sport, built for the 1960 Olympic Games in Rome, is made of concrete. But it was the geodesic dome, invented by Richard Buckminster Fuller in 1947, that changed the modern dome altogether. A geodesic line is the shortest distance between two points across a curved surface. Buckminster Fuller noticed that the surface of a sphere could be divided into triangles by a network of geodesic lines, and he used this idea to create a structure that was roughly spherical, but made up of many light, straight supports. The first such dome to be built was the Dome of Discovery, constructed for the Festival of Britain in 1951.
It is difficult to see why builders should ever stop using domes. They have dominated skylines around the world for 2,000 years, lending importance to the functions nd rites that take place beneath them. All kinds of people, from popes to town councillors, have taken advantage of these properties. It seems likely that the practicality of domes, combined with their awe-inspiring beauty, will assure their survival into the next millennium.
* Make a geodesic dome - see The GlobalVillage, centre pages.
* Christian architecture, the hemisphere symbolises the cosmic canopy. The Western church builders of the Middle Ages used the soaring spire to draw the thoughts of worshippers up to heaven. In the East, by contrast, the eye of God looked from an overarching dome, richly decorated with stars or images of saints and angels, and jewelled with gilding and mosaic. The church of Hagia Sophia, in Byzantine Constantinople - later a mosque and now a museum - was the largest and most splendid of these domed Byzantine churches.
Muslim builders also recognised the potent imagery of the dome. The earliest surviving Islamic monument is the Dome of the Rock, in Jerusalem. It was built in 691AD to mark the place where the Prophet ascended into heaven and the building's shape reminds worshippers of the event.
Another dome, of white marble, was built by Shah Jahan as the mausoleum of his much-loved wife. This is the famed Taj Mahal at Agra in northern India.
DOMES THROUGH THE AGES
he Romans were the first people to construct large-scale masonry domes. The Emperor Hadrian built the Pantheon as a temple for all the Roman gods. It is a perfect dome, still standing today.
When Nero rebuilt his palace in Rome after the great fire of AD64, it included an octagonal hall with a domed roof.
With the Renaissance came a revival of interest in the styles of antiquity. The merchants of Florence drew up plans for a traditional Gothic cathedral in 1296, but by 1366 they had changed their minds and commissioned a domed building instead, constructed along classical lines. This started a fashion which culminated in the early 16th century with the rebuilding of the Basilica of St Peter in Rome. Michelangelo was involved in the design and decoration of its great dome, and his work can still be seen.
The vogue for classically inspired churches took longer to reach Northern Europe. It was nearly 200 years later, in 1675, that Sir Christopher Wren designed a dome as the central feature of the new St Paul's Cathedral. Russian churches, influenced by Byzantium, also incorporated the dome. The Byzantine style fused with local traditions to produce the brightly painted, onion shaped domes which can be seen in the Kremlin in Moscow. This is the site of the Cathedral of St Basil, built by Ivan the Terrible to commemorate his victory over the Tartars in 1547. It is said that the eight domes of the cathedral represent the eight turbanned Muslim chieftains whom he beheaded after his victory.