On June 26, 2001 the CN Tower, the World's Tallest Building and Free Standing Structure celebrated its 25th Anniversary. Defining the Toronto skyline, the CN Tower is Canada's most recognizable and celebrated icon, an important telecommunications hub, and the centre of tourism in Toronto.

At a height of 1,815 feet or 553 metres, the CN Tower has maintained its designation as the World's Tallest Building and Free Standing Structure for a record 25 years. A feat that has not gone unnoticed. The CN Tower was built in 1976 by Canadian National (CN) who wanted to demonstrate the strength of Canadian industry by building a tower taller than any other in the world.

Before the CN Tower was built, the Ostankino tower, built in Moscow, was the tallest free-standing structure on the planet, at a sky-spearing 1,762 feet or 540 metres. So, here on Canadian soil, officials decide to go for it. To make what would later be christened the CN Tower, the tallest of the tall. They added about 100 extra feet - or 30 metres - at a cost of less than $200,000, says project architect Ned Baldwin, who was with John Andrews Architects.

CN Tower construction crews moved in on February 6, 1973, and started to remove over 56 metric tonnes of earth and shale for the foundation. Once the foundation was ready, work began on the CN Tower’s 335 m (1,100ft.) concrete shaft, a hexagonal core with three curved support arms. This involved pouring concrete into a massive mold or "slipform". As the concrete hardened, the slipform, supported by a ring of climbing jacks powered by hydraulic pressure, moved upwards, gradually decreasing in size to produce the CN Tower’s gracefully tapered contour.

Eight months later, the CN Tower’s concrete shaft was the tallest structure in Toronto and by February 1974, it was the tallest in Canada. In August 1974, work began on the seven-story tower sphere that would eventually house the observation decks and revolving restaurant. The CN Tower approached completion in March 1975, when Olga, the giant Russian Sikorsky helicopter flew into the city to lift the 44 pieces of the antenna into place.

On April 2, 1975 when the OLGA helicopter lifted the 44th and final piece of the CN Tower's antenna into place, the CN Tower joined the ranks of 17 other great structures that had previously held the title of World's Tallest Free-Standing Structure. Ross McWhirter, editor of the Guinness Book of World Records, was on hand to record the milestone for history and since then, the CN Tower has received numerous mentions in the famous book including the World’s Longest Metal Staircase and most recently, the World’s Highest Wine Cellar. In 1996, the CN Tower’s classification was officially changed to the World’s Tallest Building and Free-Standing Structure.

The cost then to build the CN Tower was $63 million,  approximately $300 million today. It was an ambitious project that involved 1,567 workers who worked 24 hours a day, five days a week for 40 months to completion.

After 40 months of construction, the CN Tower was finished on April 2, 1975 and opened to the public on June 26, 1976. Although less than one year old, it was well on its way to becoming the country’s most celebrated landmark. Twenty-five years later, it is the centre of telecommunications for Toronto serving 16 Canadian television and FM radio stations, the workplace of up to 550 people throughout the year, and one of Toronto’s premier entertainment destinations.

In 1995, the CN Tower was classified as one of the Seven Wonders of the Modern World by the American Society of Civil Engineers. The World’s Tallest Building shares this designation with the Itaipu Dam on the Brazil/Paraguay border, the Golden Gate Bridge in San Francisco, the Panama Canal, the Chunnel under the English Channel, the North Sea Protection Works off the European coast, and the Empire State Building.

Since the CN Tower opened, Canadians and tourists from around the world have made the trip to Toronto to celebrate this marvel of civil engineering. Besides serving as a telecommunications hub, the CN Tower provides world-class entertainment and a wide range of unique attractions, exhibits and food and beverage venues.

In past years, the CN Tower has supported its vision of Toronto’s premier entertainment destination by totally renovating and redesigning 360 Restaurant, building the World’s Highest Wine Cellar, and adding two new elevators.

Main Source: www.cntower.ca

Some interesting facts:

* CN Tower was created to solve a problem. In the late 1960s, watching television, there were blurred pictures, caused by a growing number of high-rise buildings, interfering with transmission signals. This new super-high tower solved the problem.

*The CN Tower has 102-metre antenna, which was raised segment by segment.

*Total weight of the tower is 117,910 metric tones.

*The revolving restaurant sways up to one metre in high wind. Nicholas Isyumov, 65, knows all about that. He worked for seven years studying models for the tower and predicting how it would stand up in the wind.

“It can sway up to 12 feet (3½ metres) at the top, but on a normal day, the motions are much smaller than in a typical tall building. It’s a very safe place to come,” he says.

*CN Tower has an extensive sprinkler system, a 24-hour monitoring operation, and two 68,000-litre water reservoirs at the top of the building. There is also a firehose at the tower’s base, which can send 2,700 litres of water a minute to any location.

*The elevator at the CN Tower runs up the outside of the building and can be powered by emergency generators.