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 and structures in London
The history of tall structures in London began with the completion of the White Tower, a part of the Tower of London, in 1098. The first structure to surpass a height of was the Old St Paul's Cathedral. Completed in 1310, it stood at a height of . St Paul's was the world's tallest structure until 1311, when its height was surpassed by Lincoln Cathedral in Lincoln. It regained the title when the spire of Lincoln Cathedral fell in 1549. Although the spire of the Old St Paul's was destroyed by lightning in 1561, it still stood as the tallest structure in London, while the world's tallest structure became Strasbourg Cathedral in Strasbourg, France. St Paul's was severely damaged by the Great Fire of London in 1666. The title of the tallest structure in London passed to Southwark Cathedral, which stands at a height of and no structure in London again rose above 100 metres until 1710, when the current St Paul's Cathedral was completed. At , the cathedral remained London's tallest building until it was overtaken in 1962 by the BT Tower, which was topped out in 1964 at and officially opened in 1965.