Willis Tower

A 110-story skyscraper in Chicago, completed in 1973 as the Sears Tower. Its bundled-tube structure made it one of the world’s tallest buildings.

Bundled tube: A structural system that joins several framed tubes to resist a tall building’s wind and gravity loads. This system gives the tower its distinctive form and structural strength.
Sears: An American retail company that grew into one of the country’s largest department-store chains. Sears commissioned the building as its headquarters and gave it its original name.
Willis Tower Skydeck: An observation deck on the 103rd floor of Willis Tower, featuring glass balconies called the Ledge. Skydeck turns the tower’s height into a public attraction and viewing experience.
Tallest buildings in the world: A changing group of buildings ranked by height under specified measurement rules. Willis Tower held the world’s tallest-building title for nearly 25 years.
One World Trade Center: A 104-story skyscraper in Lower Manhattan, completed in 2014. It later surpassed Willis Tower as the tallest building in the United States by architectural height.
Skyscraper: A tall, continuously habitable building whose height demands specialized structural and vertical-transport systems. Willis Tower is a landmark example of the skyscraper.
Chicago: A major city in Illinois, United States, on the southwestern shore of Lake Michigan. The tower’s site, skyline, and architectural context are rooted in Chicago.
The Ledge: A set of glass-floored balconies extending from Willis Tower’s Skydeck. These balconies let visitors look directly down the tower’s exterior.
List of tallest buildings in the United States: A ranking of buildings in the United States by height. The tower remained the country’s tallest building for decades after its completion.
Petronas Towers: Twin 88-story skyscrapers in Kuala Lumpur, completed in 1998. They became the world’s tallest buildings by architectural height after Willis Tower’s reign.

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