During the last decades, mega-events have been an instrument
through which cities around the world have developed part of their
urban plans and projects. They have also become an essential element
of its foreign marketing policy and its growth and transformation strategies.
However, not all the changes produced by these mega-events
are positive and there are numerous criticisms for their high economic,
environmental and social cost. Of all of them, the World Expos and the
Olympic Games are those that after their celebration leave a deeper
mark on the economy, image, society and urban planning of their host
cities, acting as urban catalysts. Therefore, they are the events that
are discussed in this work as well as their preparation, transformations
and legacy, providing a historical vision of them. Through a case study,
the urban impact of the London 2012 Olympic Games, the 2015 Milan
Expo and the Tokyo 2020 Olympics is shown, also analyzing the urban
history of the japanese capital city.