August 7 - The Duomo, Florence

On August 7, 1420, construction began on the dome (Duomo) of the Basilica di Santa Maria del Fiore (Basilica of Saint Mary of the Flower) in Florence, Italy. The structure was engineered by architect Filippo Brunelleschi, who had won a competition sponsored by the city’s wool merchants’ guild, which had fears about building a dome above the 140-foot octagonal space already built to support it. No dome that wide then existed except Rome’s Pantheon, which is supported on massive walls. The competition involved great architects attempting to stand an egg upright on a marble slab. Brunelleschi succeeded by striking one end of an egg sharply on the flat marble, leaving it upright. His dome contains two shells, whereby workers sat atop the inner, lightweight shell to build the heavier outer shell. Rings hug both shells of the octagonal dome, and supporting “ribs” run through the rings. The herringbone pattern of the brick structure transfers weight to the supports. The project, structurally completed in 1436, and its crowning lantern occupied most of Brunelleschi’s life.