It's interesting to note that Toronto's CN Tower is basically a single piece of concrete up to the top. After the foundation was set the main column of the building was created by pouring concrete into a mold. Once the concrete had partially set, the mold was raised and more concrete was poured on. The concrete mold was brought up higher and higher as the base of the building set and concrete was poured continuously day and night until the CN Tower was complete up to the first observation deck. The concrete could never be allowed to dry completely as this would negatively affect the structural stability, which was of paramount concern for such a grandiose and risky design. This is how the CN Tower was made so quickly - in under four months! In the later stages of construction, concrete had to be brought up to the mold via helicopter. It's true!