The Calgary Tower is a free standing observation tower in the downtown core of Calgary, Alberta, Canada. Originally called the Husky Tower, it was conceived as a joint venture between Marathon Realty Company Limited and Husky Oil as part of an urban renewal plan and to celebrate Canada's centennial of 1967. The tower was built at a cost of and weighs approximately 10,884 tonnes, of which 60% is below ground. It opened to the public on June 30, 1968 as the tallest structure in Calgary, and the tallest in Canada outside Toronto. It was renamed the Calgary Tower in 1971. The building was a founding member of the World Federation of Great Towers. History Planning and construction The project was originally conceived as a joint venture by Marathon Realty (the real estate subsidiary of Canadian Pacific Railways) and Husky Oil for their new head offices in Calgary. They proposed building the tower both to honor Canada's centennial year of 1967 and to encourage urban renewal and growth of downtown Calgary. The structure was designed by A. Dale and Associates, and was designed to withstand earthquakes and winds of up to . The urban renewal project was announced to the public on December 10, 1965 and consisted of a transport terminal, hotel, parking, office facility and a 550 foot "restaurant-observation tower". The chosen site housed Canadian Pacific's Calgary passenger station which was demolished a year after the announcement to make way for the development. The provincial government reviewed the tower proposal for consideration as a publicly funded centennial project, but Public Works Minister Frederick C. Colborne recommended against the use of public funds for the project. The concept of a centennial tower was originally proposed for Edmonton, but the project was opposed by residents near the chosen site. Former Calgary Mayor Grant MacEwan asked the provincial government to move the project to Calgary, until Marathon and Husky decided to build the project independent of public funds. The plan for the tower continued to change as construction delays occurred and the planned height rose from 550 feet to 600 feet. Construction began on February 19, 1967, and completed in 15 months at a cost of . The column of the tower was built from an unprecedented continual pour of concrete. Pouring began May 15, 1967 and was completed 24 days later at an average growth of per day, a rate that was