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Since its completion in 1976, the 553.3-metre CN Tower in Toronto has enjoyed the distinction of being the world's tallest free-standing structure.

When the CN Tower project was first announced, it seemed almost impossible. At the time, the Toronto skyline was dotted with monolith buildings, the highest of which was already over 228 metres. Toronto's ascending skyline posed a problem for existing communications systems since pre-skyscraper transmission towers were simply not high enough to broadcast over the new obstacles.

Construction of the Tower began on February 6, 1973. First, over 56,000 metric tons of earth and shale had to be removed, for the 15-metre deep concrete and steel foundation. Seated on a base of shale, the Y-shaped foundation contains over 7,000 cubic metres of concrete and 450 metric tons of reinforcing steel. Four months after construction first began, all was ready for the above-ground operation. Twenty-four hours a day, five days a week, concrete was poured into a massive mold or "slipform". As the concrete hardened, the "slipform" was moved upwards, gradually decreasing in size to produce the gracefully tapered contour of the Tower. The three concrete legs that were thus formed are hollow, while the hexagonal core houses all of the electrical cables and water piping.

In August, 1974, work began on the seven-storey SkyPod, which would ultimately house two observation decks, the 360-degree revolving restaurant, a bar, and various other entertainment and technical areas. At its base, the SkyPod has a donut-shaped collar technically known as the radome, which protects the sensitive microwave communication dishes from the elements. Made of teflon-coated, fibreglass-rayon fabric, its balloon-like shape is the result of inflating the skin to five times its normal size, then maintaining constant air pressure.

In February, 1974, the concrete portion of the Tower was completed. Situated at the top of the concrete is the world's highest public observation gallery, called the Space Deck. Extending above it, is the hollow, 102-metre steel antenna.

Erecting the enormous antenna presented a special challenge to the designers of the Tower. The solution was a giant Sikorsky helicopter, "Olga", which lifted into place, with remarkable precision, the 39 pieces of the antenna — the heaviest of which weighed more than seven metric tons.

With the placement of the 36th piece of the antenna mast, on March 31, 1975, the CN Tower surpassed Moscow's Ostankino Tower, to become the world's tallest free-standing tower. On hand to record the milestone was Ross McWhirter, then editor of The Guinness Book of World Records of London, England. In December of 1995, the CN Tower was acknowledged as one of the Seven Wonders of the Modern World by the American Society of Civil Engineers.

Today, the CN Tower welcomes approximately 1.7 million Canadian and international visitors annually. Both public and experts from the field of construction come to marvel at the Tower, which stands as a testament to human ingenuity and achievement. While some day, some place, someone might build a tower higher, the significance of the CN Tower to the people of Canada and to visitors worldwide will never be diminished.