CHICAGO - APRIL 22: The Willis Tower on April 22, 2008 in Chicago, Illinois. Built as the Sears Tower, its 110 stories standing 1,450 feet high made it the world's tallest from 1973 to 1998.
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CHICAGO - APRIL 22: The Willis Tower on April 22, 2008 in Chicago, Illinois. Built as the Sears Tower, its 110 stories standing 1,450 feet high made it the world's tallest from 1973 to 1998.