But there was a problem: Mies' design for the Brussels pavilion had to please Hitler's regime. So he did his best in the circumstances. He added four flagpoles with swastika banners. He stuck a German eagle over the entrance. He Nazified his building. There is the drawing of it, in his own hand, in the Whitechapel exhibition. Had he won the competition, the subsequent career and reputation of Mies would have been very different. But it was rejected - some say, by Hitler personally. That was the end of official German patronage of Mies. Soon after, he was given a house commission in America, and later offered a teaching post in Chicago. He packed up his portfolio and got on the ship. Rather later than some of his illustrious contemporaries and friends such as Walter Gropius or Erich Mendelsohn. In the post-war years the Mies style came to characterize corporate America and he became even more famous. He did not return to Berlin until the mid 1960s, when he designed the new National Gallery in the western sector. He died in 1969, aged 83.

Since when, he has been in and out of fashion. Possibly no other architect inspires such devotion among his disciples, who will argue for hours about the precise spacing of a column or the way he turns an outside corner or arranges beams or makes a staircase appear to float. To such people, Mies is a deity, and to recount his efforts to accommodate Nazism is akin to blasphemy. Certainly it is skimmed over rapidly by the Whitechapel exhibition, which originates from the holder of the Mies archive, New York's Museum of Modern Art.

But what of the work? Mies, like Le Corbusier, has suffered from second-rate imitations which degrade the impact of the original. The world is full of 1950s and 1960s "Miesian" office blocks. I still remember the stab of disappointment I felt when I first saw his celebrated Seagram building (1956-9) in New York. Was that dull thing what all the fuss was about?

The appeal of the Whitechapel show is that it is devoted entirely to Mies in his pre-American phase. When he was developing his approach, when he was making his name, before he was coasting. From the earliest designs, we see the Mies tabula rasa approach in action. There is no context to these buildings. They stand alone, they always have a buffer zone around them, they do not touch or acknowledge anything else. Landscape is altered to fit them, itself becoming architecture. This is arrogant, self-centred architecture for sure: buildings as sculpture, up on a plinth. But some of them approach perfection. From early exercises in relating buildings to their landscapes, such as the Perls House in Berlin, through to the Barcelona Pavilion, the Tugendhat House in Brno, Czech Republic, the early unbuilt 1920s designs for glass skyscrapers in Berlin, his highly personal 1930s sketches of a mountain retreat that influenced a whole generation of post-war architects.