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).
History of the world's tallest buildings
Since the completion of the Washington Monument in 1884, the world's tallest building has not usually also been the world's tallest "structure". The exceptions are 1930–1954, when the Chrysler Building and then the Empire State building surpassed the Eiffel Tower (to be surpassed in turn by a succession of broadcast masts, starting with the Griffin Television Tower in Oklahoma), and from 2010 with the completion of Burj Khalifa.