Cathedral of Santa Maria del Fiore

Here's the thing about Brunelleschi's dome: nobody thought it could be built. When Florence decided to cap their cathedral with the largest dome since the Pantheon, they had no idea how to actually do it. The hole sat open to the rain for decades. Then Filippo Brunelleschi — a goldsmith with no formal architecture training — proposed building it without scaffolding or centering, and everyone thought he'd lost his mind. He won the commission anyway, partly because nobody else had a better idea.

What Brunelleschi invented was essentially a self-supporting structure using a herringbone brick pattern that locked each layer into the one below. He designed custom hoisting machines, including an ox-driven crane that could reverse direction without unhitching the animals. The dome rose over sixteen years, from 1418 to 1434, using over four million bricks and weighing roughly 25,000 tons. It remains the largest masonry dome ever constructed.

Inside, Giorgio Vasari and Federico Zuccari covered the dome's interior with a massive Last Judgment fresco — 3,600 square meters of apocalyptic imagery hovering above the nave. The cathedral itself took 140 years to complete, from 1296 to 1436, and could hold 30,000 worshippers. When it was consecrated, it was the largest church in the world.

Stand outside and look up. That dome has dominated Florence's skyline for nearly six centuries. Brunelleschi is buried in the crypt below — one of only a handful of people granted that honor — and his tomb was only discovered in 1972.