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For 142 years now, Sagrada Família has been growing toward the sky. Or at least that’s what it seems to be doing, as its ongoing construction realizes ever more fully a host of forms that look and feel not quite of this earth. It makes a kind of sense to learn that, in designing the cathedral that would remain a work in progress nearly a century after his death, Antoni Gaudí built a model upside-down, making use of gravity in the opposite way to which we normally think of it as acting on a building. But as architecture YouTuber Stewart Hicks explains in the video above, Gaudí was hardly the first to use that technique.

Take St. Paul’s Cathedral, which Christopher Wren decided to make the tallest building in London in 1685. It included what would be the highest dome ever built, at 365 feet off the ground. “For a traditional dome design to reach this height, it would have to span an opening that’s 160 feet or 49 meters wide, but this made it much too heavy for the walls below,” says Hicks. “Existing techniques for building this just couldn’t work.” Enter scientist-engineer Robert Hooke, who’d already been figuring out ways to model forces like this by hanging chains from the ceiling.

“Hooke’s genius was that he realized that the chain in his experiments was calculating the perfect shape for it to remain in tension, since that’s all it can do.” He explained domes as, physically, “the exact opposite of the chains. His famous line was, ‘As hangs the flexile line, so but inverted will stand the rigid arch.’ ” In other words, “if you flip the shape of Hooke’s chain experiments upside down, the forces flip, and this shape is the perfect co*pression system.” Hence the distinctively elongated-looking shape of the dome on the co*pleted St. Paul’s Cathedral, a departure from all architectural precedent.

The shape upon which Wren and Hooke settled turned out to be very similar to what architecture now knows as a catenary curve, a concept important indeed to Gaudí, who was “famously enamored with what some call organic forms.” He made detailed models to guide the construction of his projects, but after those he’d left behind for Sagrada Família were destroyed by anarchists in 1936, the builders had nothing to go on. Only in 1979 did the young architect Mark Burry “imagine the models upside-down,” which brought about a new understanding of the building’s co*plex, landscape-like forms. It was a similar physical insight that made possible such dramatic mid-century buildings as Annibale Vitellozzi and Pier Nervi’s Palazzetto dello Sport and Eero Saarinen’s TWA Flight Center: pure Space Age, but rooted in the Enlightenment.

Related content:

How the World’s Biggest Dome Was Built: The Story of Filippo Brunelleschi and the Duomo in Florence

How This Chicago Skyscraper Barely Touches the Ground

Why Hasn’t the Pantheon’s Dome Collapsed?: How the Romans Engineered the Dome to Last 19 Centuries and Counting

An Architectural Tour of Sagrada Família, Antoni Gaudí’s Audacious Church That’s Been Under Construction for 142 Years

A Guided Tour of the Largest Handmade Model of Imperial Rome: Discover the 20x20 Meter Model Created During the 1930s

Based in Seoul, Colin Marshall writes and broadcasts on cities, language, and culture. His projects include the Substack newsletter Books on Cities and the book The Stateless City: a Walk through 21st-Century Los Angeles. Follow him on Twitter at @colinmarshall or on Facebook.