Now known as the Willis Tower and no longer the world’s tallest building, this structure will nevertheless always enjoy the distinction of having been the Sears Tower, and of having been the world’s tallest building, in a time when both name recognition and world record fame were not so fleetingly won and lost. The Willis Tower was also the last of the extremely tall skyscrapers built in Chicago during the International period.
The building’s nine interlocking tubes provide a structural bracing system, but they are also responsible for the building’s stepped-back appearance. At the base the tubes form a nine-square grid in plan, but as the building height increases, only select squares are continued upward.
