Over the octagon of some forty-five meters left open at the crossing of Santa Maria del Fiore, Filippo Brunelleschi raised the largest masonry dome ever built, between 1420 and 1436 and without centering. It has two shells, the inner one the thicker, bound by ribs and hooped with chains of stone and timber. They rise on a pointed profile that tempers the thrust. In every course, bricks set in herringbone locked the ring being laid, so that the structure carried itself at every stage of the work. Begun in 1296 by Arnolfo di Cambio on the site of Santa Reparata, the cathedral was awaiting a crown whose form had been settled since 1367. It was the form of Neri di Fioravanti's model: a double-shelled dome without flying buttresses that no one yet knew how to build, and which the officials of the works swore to uphold. A goldsmith by training, Brunelleschi prevailed after the competition opened in 1418. Pope Eugene IV consecrated the church on 25 March 1436, and the lantern Brunelleschi designed rose only after his death. Re-traced the cathedral by hand, in archival ink, as a longitudinal section. Taken along the axis of the nave, the section cuts the dome through its center and lays open the hidden space between the two shells. Detailed down to its play of light and shadow, it is surmounted by a plan at a smaller scale.