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For decades, the greatest church in Florence stood open to the sky. There was a hole at its centre, forty-five metres across, and nobody alive knew how to close it… They had done it on purpose. A model approved in 1367 called for a dome wider than any built since ancient Rome, and the Florentines put up the walls anyway, leaving the problem to whoever came next. The Roman method had been lost for a thousand years. Every dome since had been raised on centering, an enormous wooden scaffold built underneath to hold the masonry until it set. For a span this size, no forest in Tuscany could supply the timber. So the cathedral waited, with rain falling into it… In 1418 the city announced a competition. A goldsmith named Filippo Brunelleschi told them he would build the dome with no centering at all. The masonry would hold itself up as it rose. Many of his contemporaries decided he was a lunatic. One rival, Giovanni da Prato, wrote a public sonnet calling him a "dark, deep wellspring of ignorance" and a "miserable and imbecile beast," and rashly promised to kill himself if the plan ever worked. Brunelleschi answered with a sonnet of his own, advising him to destroy his poems, "lest they sound ridiculous when all the dancing starts, in celebration of that which he now thinks impossible." It took sixteen years. Over four million bricks, laid in a herringbone pattern so each ring locked and carried itself, in two shells, one inside the other, weighing something over twenty-five thousand tons. He designed the hoists that lifted the materials, machines Leonardo da Vinci would later sit and copy into his notebooks. It was finished in 1436. Six hundred years later it is still the largest masonry dome on earth… The director Franco Zeffirelli, a Florentine, once said what that dome does to a person who looks up at it: "When I feel depression creeping in, I return to Florence to gaze at Brunelleschi's dome. If human genius was able to achieve something so great, then I too can and must try to create, to act, to live."