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 (née 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.