This content was created in partnership with Aerial Cities, a new show on Smithsonian Channel that explores America's most prominent cities from breathtaking heights. Watch the series Sundays at 8/7c.
From the day it opened in 1973 until it was eclipsed by Malaysia's Petronas Towers in 1998, the Willis Tower (Maiden name: Sears Tower) was the tallest building in the world. Constructing it was a major feat of engineering, because once you get a building that far off the ground, the wind can really start to mess with its structural integrity. And Chicago isn't called the Windy City for nothing.