At 1,450 feet, it had more space and was higher than the Empire State Building. The Sears Tower was the first building to use this design.

The last west and center tubes reach 108 floors. The northeast and southwest tubes reach the 66th floor with the north, east, and south tubes end at the 90th. All nine tubes would rise up to the 50th floor of the building, where the northwest and southeast tubes end. It was connected in a 3Г—3 metal wrap forming a square base with 225-foot (69В m) sides. They designed it as a nine square ' tubes'. Architects Bruce Graham and Fazlur Khan designed the building. Sears paid for construction of the building. They hired architects Skidmore, Owings & Merrill (SOM). Sears needed 3В million square feet (280,000В m 2) of office space for its planned tower. Sears and the city of Chicago approved the design and construction began in April 1971. Sears eventually bought the West Chicago loop location and bought 15 old buildings from 100 owners and paid $2.7 million to the city. The company was given a location by West Chicago Loop not far from Grant Park. Sears wanted to put many of its employees into one building on the western part of Chicago's Loop. was the largest retailer in the world, with about 350,000 employees. Many people from Chicago still call the tower by its original name. It was known as the Sears Tower until 2009, as it was the headquarters of retail company Sears from its opening in 1974. Morgan Stanley moved into the tower in 2019. Other major company offices in the tower include Schiff Hardin and Seyfarth Shaw. The building's largest office partner is United Airlines, which moved its corporate headquarters from 77 West Wacker Drive in 2012. The tower was renamed in 2009 after the Willis Group bought the tower. It is one of Chicago's most popular tourist places. Each year, more than one million people visit its observation deck, the highest in the United States.

It is also the 23rd-tallest in the world. As of 2021, it is the third-tallest building in the United States and the Western hemisphere. Willis Tower is seen as the best work of architect Fazlur Khan. It was also the tallest building in the Western Hemisphere for 41 years, until the new One World Trade Center beat it in 2013. It was the tallest building in the world for twenty-five years until the Petronas Towers were built in Malaysia. When it finished costruction in 1973, it beat the World Trade Center in New York City to become the tallest building in the world. The tower has 108 stories, though the building's owners count the main roof as 109 and the mechanical penthouse roof as 110. The Willis Tower, formerly known as the Sears Tower, is a 108- story, 1,450-foot (442.1В m) skyscraper in Chicago, Illinois. Location in the United States Show map of the United States

Sears tower