The octagonal dome that was to crown Santa Maria del Fiore, the cathedral begun in Florence in 1294, presented the most daunting architectural puzzle of the age: how to raise the highest and widest vault ever attempted. The cupola was to have a span greater than the Roman Pantheon—the world’s largest dome—and vaulting higher than any Gothic cathedral. The logistical problems were enormous. How could this enormous octagonal structure be made self-supporting? How could the tons of masonry be raised more than 200 feet in the air and laid into place with micrometric accuracy? This illustrated lecture examines the procedures developed by Filippo Brunelleschi as he worked on the dome between 1420 and 1436, successfully executing what is still the world’s largest masonry dome.