In 1851, the date of the first World Expo, electricity was not yet used for lighting or as a power source, the internal combustion engine did not exist, neither the radio nor the telephone had been invented, and the first motorised aeroplane had yet to take off. In architecture, the use of industrial iron was just beginning, while steel was not yet used in building. Reinforced concrete had not been invented. Stone, wood and brick were still the main construction materials used. Since this date, Expos have borne witness to and been the venue of the advances that have transformed the world which we know today.