In 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 splendi 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.