The CN Tower

The CN Tower, located in downtown Toronto, Ontario, Canada, is a communications and tourist tower standing 553.33 metres (1,815.39 ft) tall. It surpassed the height of the Ostankino Tower while still under construction in 1975, becoming the tallest free-standing structure on land in the world. On September 12, 2007, after holding the record for 31 years, the CN Tower was surpassed in height by the still-under-construction Burj Dubai. It remains the tallest free-standing structure in the Americas and the signature icon of Toronto's skyline, attracting more than two million international visitors annually. 'CN Tower' stands for Canada's National Tower. The CN Tower consists of several substructures. The main portion of the tower is a hollow concrete hexagonal pillar containing the six elevators, stairwells, and power and plumbing connections. On top of this is a 334.6 ft metal broadcast antenna, carrying TV and radio signals. There are two visitor areas: the main deck level (formerly known as SkyPod) located at 346 metres (1,135 ft), and the higher Sky Pod (formerly known as "Space Deck) at 1,465 ft, just below the metal antenna. The hexagonal shape can be seen between the two areas; however, below the main deck, three large supporting legs give the tower the appearance of a large tripod. Construction on the CN Tower began on February 6, 1973 with massive excavations at the tower base for the foundation. By the time the foundation was complete, 56,000 tonnes (61,729 short tons) of dirt and shale were removed to a depth of 49.2 ft in the centre, and a base incorporating 7,000 cubic metres (9,156 cu yd) of concrete with 450 tonnes (496 short tons) of rebar and 36 tonnes (40 short tons) of steel cable had been built to a thickness of 22 ft.