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Designed by Graham and Khan
The tower was designed by the architect Bruce Graham and the structural engineer Fazlur Rahman Khan of Skidmore, Owings & Merrill. Its structure is a bundle of nine square tubes arranged three by three, the first design of its kind, and an idea since used in many of the world’s tallest buildings.


Built from 1970 to 1974
Construction began in 1970. The tower was topped out on 3 May 1973 and opened that September as the Sears Tower, the tallest building in the world, a title it held until 1998. Work on the building was completed in 1974.
The Skydeck and The Ledge
The Skydeck opened on 22 June 1974 on the 103rd floor, 1,353 feet (412 metres) above the street. On 2 July 2009 The Ledge opened: glass boxes that reach about four feet (1.2 metres) out from the side of the building. That same month the tower was renamed Willis Tower.


