World Fairs have been big affairs since the mid-1800s. Technically, it's not an official, traveling event like, say, the Olympics, which has an international committee and a standard, every-four-year format. International expos are regulated by the Bureau International des Expositions in France, and are rooted in England's Great Exhibition of 1851.
The idea was to showcase the latest innovations in science and technology - products of, and tools that would catalyze, the industrial revolution. Here are some of the architectural remnants of World's Fairs passed.