construction of the concrete tower started on february 6, 1973. in 1975, while it was still being built, it became taller than the ostankino tower in moscow. when it opened to the public on june 26, 1976, it became the tallest free-standing structure on land in the world. it held this record for more than thirty years, until the burj khalifa, while it was still being built, became taller on september 12, 2007 . the cn tower continued to be the world's tallest tower until the canton tower became taller in 2010. it is now the ninth tallest building in the world and the fifth tallest free-standing structure behind both of these, the shanghai tower, and the burj khalifa.