The CN Tower in Toronto was designed by John Andrews and the firm Webb Zerafa Menkès Housden, with NCK Engineering as structural engineer. Construction began on February 6, 1973, and the tower opened on June 26, 1976. It was built to carry television and radio broadcasts, because nearby skyscrapers had weakened the signals and called for taller antennas.
It stands 1,815 feet (553.3 m) high and was the world's tallest freestanding structure from 1975 until 2007. A hollow concrete shaft, hexagonal in section, rises from a Y-shaped base formed by three legs. The main pod holds the SkyPod, at 1,465 feet (446.5 m), below a 335-foot (102 m) metal antenna that a helicopter lifted into place in 36 sections.
A glass floor at 1,122 feet (342 m) was added in 1994, and the EdgeWalk, a tethered walk around the main pod at 1,168 feet (356 m), opened in 2011.
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