The German Pavilion at the 1929 World's Fair in Barcelona holds the record for fame per m2 built. A flat roof, 8 metal posts and a dozen walls. How and why did this minimal structure come to embody twentieth-century modernity? Apart from its iconic dimension, the Pavilion had no other function than to host a one-off reception for the King and Queen of Spain, for less than an hour, on the opening day of the exhibition. Here, Mies van der Rohe gives his own vision of the new architecture.