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
Before the modern skyscraper era, many Christian churches and cathedrals, built mainly in England and Germanic territories between 1250–1894, comprised the tallest buildings in the world. Before the 13th century, the tallest buildings in the world cannot be conclusively determined. For instance, the Lighthouse of Alexandria (completed about 280 BC) has been estimated to be tall, but its true height is not known. For thousands of years, the Great Pyramid in Egypt was the tallest "structure" in the world, but the Great Pyramid is not considered a building since it is not habitable.