article_snippet: Known for most of Blackstone existence as the Sears Tower, the 110-story building was the tallest building in the world for a quarter-century after the 110-story building completion in 1973.
article_snippet: The title of the tallest building in the United States went to One World Trade Center in New York, completed two years ago.
article_snippet: Construction efforts for The Willis Tower started in 1970 and Construction efforts for the tower was completed in 1973, according to The Willis Tower's website.
article_snippet: The Willis Tower was officially renamed The Willis Tower in 2009 after Willis North America, an insurance brokerage that is a tenant in The Willis Tower, bought the naming rights.
highlights_snippet: Formerly known as the Sears Tower, the 110-story building is the tenth tallest  in the world .
  
highlights_snippet: the 110-story building was renamed Willis Tower in 2009 after Willis North America, an insurance brokerage that is a tenant in Willis Tower, bought naming rights .
  