There is a photograph of Mies van der Rohe talking to King Alfonso XIII of Spain. It was taken in May 1929 during the opening ceremony for Mies’s German Pavilion, built for that year’s World Fair in Barcelona. Both men are in morning dress, clutching top hats and standing in the shade of the pavilion’s slab roof. Here is a collision of the 19th and 20th centuries – men in white gloves inspecting a free-flowing pavilion, not so much a building as a sculpture, with no purpose beyond giving form to Mies’s ideas. In one building, modernism entered the stage of high politics.

Ludwig Mies van der Rohe (he added the aristocratic-sounding ‘van der Rohe’ in 1921 to disguise his family’s background as stonemasons) was already forty-three at the time he designed the German Pavilion. He was far from an architectural prodigy, having had a long apprenticeship designing conventional country houses for the German bourgeoisie during the 1900s and 1910s. Even so, the world of Alfonso XIII was not entirely alien to Mies: the first house he designed, for the philosopher Alois Riehl in 1908–9, was engineered in such a way that its owner could look down on Emperor Wilhelm II as he travelled between Schloss Glienicke in Berlin and Schloss Babelsberg in Potsdam. It was a move of ostentatious contempt on Riehl’s part, which nevertheless spoke to a Europe where monarchs still bent the world towards them.

Even at his most avant-garde, Mies was able to construct buildings that appealed to bankers, royalty, diplomats, heiresses and industrialists. He moved comfortably in such circles. This, perhaps, was the secret of his success. The German Pavilion itself was bound up with the politics of interwar Europe. It was financed