CN Tower

• 1. Introduction

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  The CN Tower stands 553.3 metres above downtown Toronto, a concrete and steel needle that held a world record for 32 years. It is a communications and observation tower, completed in 1976 on the former Railway Lands. Its name traces back to Canadian National Railway, the company that conceived, funded, and built it. What drove a railway company to construct something so far removed from laying track? And how did a structure born from broadcast needs become one of the most visited landmarks in North America, drawing more than two million international visitors each year?

• 2. A Railway's Ambition

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  In 1968, Canadian National Railway faced a problem that had nothing to do with freight. The rapid construction of skyscrapers across downtown Toronto in the late 1960s and early 1970s was degrading broadcast signals. The reflective surfaces of new buildings, including First Canadian Place which houses Bank of Montreal's head offices, bounced and scattered television and radio waves. Antennas needed to be at least 300 metres tall to clear the interference. Beyond broadcast quality, CN saw an opportunity. The tower could rent hub space for microwave data links, visible from almost any building in the Toronto area, since point-to-point rooftop dish antennas were increasingly blocked by new construction. The project became official in 1972, with CN envisioning it both as infrastructure and as a demonstration of Canadian industrial capability. From the beginning, two ambitions were woven together: the practical need for height and the ambition to build something the world would notice.

• 3. Engineering the Record

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  Construction began on the 6th of February 1973, when workers excavated the tower's foundation to a depth of 15 metres at the centre. By the time digging was done, 56,000 tonnes of earth and shale had been removed, and a base of 7,000 cubic metres of concrete reinforced with 450 tonnes of rebar and 36 tonnes of steel cable had been poured to a thickness of 6.7 metres. Workers then built a hydraulically raised slipform at the base, a large metal platform that lifted itself on jacks at roughly 6 metres per day as the concrete below cured. This continuous concrete pour ran Monday to Friday, not around the clock. By the 22nd of February 1974, the rising structure had already surpassed the 381-metre Inco Superstack in Sudbury, making it the tallest structure in Canada. The vertical accuracy achieved over the full height of the tower varies from true by only 29 millimetres, maintained by comparing the slipform's position to massive plumb bobs observed through small telescopes from the ground. The entire tower contains 40,500 cubic metres of concrete, all mixed on-site to ensure consistency between batches. On the 31st of March 1975, while still incomplete, the CN Tower officially became the world's tallest free-standing structure.

• 4. Olga and the Antenna

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  The plan was to hoist the antenna using a crane. Then the Sikorsky S-64 Skycrane helicopter, named "Olga", became available after the United States Army sold it to civilian operators. A decision was made to use the aircraft instead. Olga first removed the crane itself, then carried the antenna up in 36 separate sections. The flights were a minor tourist attraction of their own, their schedule printed in local newspapers so residents could watch. What had been estimated at six months of crane work was completed in three and a half weeks. The tower was topped off on the 2nd of April 1975, after 26 months of construction, with a total mass of 118,000 tonnes. The completed antenna is a 102-metre metal broadcast structure, its radio wire estimated at 102 metres long in 44 pieces, the heaviest of which weighs around 8 tonnes.

• 5. Life on the Observation Decks

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  When the CN Tower opened on the 26th of June 1976, visitors could choose between three public observation points. The Top, then called the Space Deck, stood at 447 metres. The Indoor Observation Level sat at 346 metres. The Outdoor Observation Terrace was at 342 metres, at the same level as what would later become the Glass Floor. One floor above the indoor level, a revolving restaurant completed a full rotation every 72 minutes. The idea for the Space Deck had come from Bud Andrews, president of the Metro Centre Developments Group, who reasoned that visitors would pay extra for the higher vantage and that construction costs were not prohibitive. When the tower first opened, it also featured a discotheque named Sparkles at the Indoor Observation Level, billed as the highest disco and dance floor in the world. From 1985 to 1992, the basement hosted the world's first flight simulator ride, Tour of the Universe, based on a Space Shuttle flight. A glass floor at an elevation of 342 metres was installed in 1994, covering an area of 24 square metres and built to withstand a pressure of 4.1 megapascals. The floor panels are 64 millimetres thick, constructed with a pane of 25-millimetre laminated glass, 25-millimetre airspace, and a pane of 13-millimetre laminated glass.

• 6. Heights, Titles, and Definitions

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  On the 12th of September 2007, Burj Khalifa in Dubai, then still under construction and known as Burj Dubai, surpassed the CN Tower's 553.33-metre height, ending a reign of more than 32 years as the world's tallest free-standing structure. The record-keeping around the tower reveals how contested such rankings can be. The Council on Tall Buildings and Urban Habitat defines a building as a structure designed for residential, business, or manufacturing purposes with floors continuously from the ground. The CN Tower, lacking continuous floors, is classified as a tower rather than a building. This distinction meant that the titles of "world's tallest building" passed instead to Taipei 101, which stands 44 metres shorter than the CN Tower. After Burj Khalifa was recognised by Guinness World Records as the world's tallest free-standing structure, Guinness re-certified the CN Tower as the world's tallest free-standing tower. That tower title then passed in 2009 to the Canton Tower in Guangzhou, China, at 604 metres, which was itself overtaken in 2011 by the Tokyo Skytree at 634 metres. The CN Tower retains several records today: it remains the tallest free-standing structure in the Western Hemisphere, holds the world's longest metal staircase at 2,579 steps, and its 360 Restaurant holds the record for the world's highest above-ground wine cellar at 351 metres.

• 7. Staircase, Storms, and Stunts

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  The metal staircase inside the CN Tower reaches the main deck after 1,776 steps and The Top after 2,579 steps, making it the tallest metal staircase on Earth. The stairs are reserved for emergency use and two charity stair-climb events per year. The fastest recorded climb, set in 1989 by Brendan Keenoy, an Ontario Provincial Police officer, stands at 7 minutes and 52 seconds to reach the base of the radome. In 2002, Canadian Olympian and Paralympic champion Jeff Adams climbed the stairs in a specially designed wheelchair. The tower has also attracted more dramatic performances. Stuntman Dar Robinson jumped from the tower twice, in 1979 and in 1980. The first jump was for a scene in the film Highpoint; the second was for a personal documentary. His first jump used a parachute deployed three seconds before impact with the ground, while the second used a wire decelerator attached to his back. On the 26th of June 1986, the tenth anniversary of the tower's opening, Dan Goodwin climbed the outside of the tower by hand and foot, then descended by rappel. He performed the climb twice in the same day. Weather has also tested the structure. On the 2nd of March 2007, a freezing rain storm left a layer of ice several centimetres thick on the tower, and winds of up to 90 kilometres per hour sent chunks flying as far as King Street West, 490 metres away, where a taxicab window was shattered. On the 16th of April 2018, falling ice from the tower punctured the roof of nearby Rogers Centre, forcing the Toronto Blue Jays to postpone their game.

• 8. A Tower in Lights and Culture

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  In June 2007, the tower was fitted with 1,330 super-bright LED lights inside the elevator shafts, shooting over the main pod and upward to the top of the mast. The official opening ceremony was held on the 28th of June 2007. The LED system uses 60 percent less energy than the brightly lit incandescent version it replaced, at an estimated cost of $1,000 per month. The tower changes its lighting to mark events: it displayed the colours of the South African flag when Nelson Mandela died, turned the colours of the French flag on the night of the Paris attacks on the 13th of November 2015, and lit in the colours of the Ukrainian flag when the Russo-Ukrainian war began in 2022. During spring and autumn bird migration seasons, the lights are dimmed under the voluntary Fatal Light Awareness Program to reduce bird mortality. The tower's lighting is programmed remotely from a desktop computer with a wireless network interface controller in Burlington, Ontario. The CN Tower has also appeared in popular culture, from the 1982 action film Highpoint, which features Dar Robinson's stunt jump, to the 2016 Drake album Views, whose cover artwork shows the rapper sitting atop the tower in a photo confirmed as edited by the tower's own Twitter account.