Dome of Santa Maria del Fiore

The cathedral had stood open to the sky for over fifty years when the Opera del Duomo announced its competition in 1418: the octagonal drum was some 45 metres across and began 55 metres above the floor, and Tuscany had no timber long enough to centre a vault of that span. Brunelleschi’s answer, begun in 1420, was to build without centring at all. Two shells, an inner structural one and an outer weather skin, are tied together by eight major and sixteen minor ribs, with stone and timber rings acting as hoops against the outward thrust; the brickwork between them is laid in a herringbone pattern so that each course locks into the last and every ring is self-supporting as it closes. Roughly four million bricks were lifted by hoists he designed himself. The shell was closed in 1436 and the cathedral consecrated the same year; the lantern was begun only after his death. It is still the largest masonry dome ever built.