CN Tower
"Guinness World Records" has called the CN Tower "the world's tallest self-supporting tower" and "the world's tallest free-standing tower". Although Guinness did list this description of the CN Tower under the heading "tallest building" at least once, it has also listed it under "tallest tower", omitting it from its list of "tallest buildings." In 1996, Guinness changed the tower's classification to "World's Tallest Building and Freestanding Structure". Emporis and the Council on Tall Buildings and Urban Habitat both listed the CN Tower as the world's tallest free-standing structure on land, and specifically state that the CN Tower is not a true building, thereby awarding the title of world's tallest building to Taipei 101, which is shorter than the CN Tower. The issue of what was tallest became moot when Burj Khalifa, then under construction, exceeded the height of the CN Tower in 2007 (see below).
List of tallest buildings in Chicago
Chicago, the third-largest city in the United States, is home to 1,315 completed high-rises, 44 of which stand taller than . The tallest building in the city is the 108-story Willis Tower (formerly the Sears Tower), which rises in the Chicago Loop and was completed in 1974. Sears Tower was the tallest building in the world from its completion, and remained the tallest building in the United States until May 10, 2013 when it was overtaken by One World Trade Center in New York City. The second-, third- and fourth-tallest buildings in Chicago are the Trump International Hotel & Tower, the Aon Center and 875 North Michigan Avenue, respectively. Of the ten tallest buildings in the United States, four are located in Chicago. Due to the contributions of Jeanne Gang and Natalie de Blois, Chicago has several of the tallest women-designed towers in the world. , the entire city had 105 buildings at least tall.