It is a Sunday afternoon in Basle, and two great architects are going to watch their local football team. Jacques Herzog and Pierre de Meuron were both born in this Swiss town in 1950, went to kindergarten together, founded an architectural firm together, designed the Tate Modern art gallery in London together, and in 2001 won the Pritzker Prize together, architecture's equivalent of the Nobel.
They support FC Basle together, don't they? "Fortunately," sighs Herzog. This afternoon they are watching as normal fans, with the slight difference that they built the stadium.
In fact, they are designing stadiums everywhere. The Munich stadium that will host the opening match of the 2006 football World Cup is theirs. So is the Beijing Olympic stadium for 2008. That same summer, Basle will be the main Swiss stadium for the European football championships, which Switzerland is hosting with Austria, and so the architects have a full house: the showpiece grounds of the world's next three biggest sports competitions. "It's totally amazing," admits Herzog.
Two days after the Basle match, in the villa where he and De Meuron started out 25 years ago, Herzog talks me through the past and future of sports grounds. He has a shaven head, gold-rimmed spectacles, a blue pinstriped jacket, yellow shoes, and is as fiery as a fan at a match.
Famous architects had never built stadiums before, he says. "It's a new issue, like museums were at some time. It was totally neglected."
So when he and De Meuron began creating stadiums, where did they look for inspiration?
"The most important model was the classical English stadium. Very often the stadium was ugly, like Old Trafford or Liverpool. But they have very interesting details, like gates or tunnels or other features which make it home for the fans. For instance, the tunnel at Liverpool where the players become aware they have to enter the field is highly architectural."
Is he thinking of the famous sign in the tunnel, "This is Anfield", which terrified generations of visiting teams? "Yes! It's about scale, it's about information, it's like a mura l. Old Trafford has something frightening, Liverpool too. But somehow, as a fan of another team you are excited. It's interesting in a modern city to create a public space which is not neutral."
The other virtue of the English stadium is how near the fans are to the pitch. "The Shakespearian theatre, probably it was even a model for the soccer stadium in England - this almost archaic closeness between the actors and the crowd. If you can achieve this proximity, the people become the architecture."
I had seen what he meant at Basle's ground that Sunday. Not only are the seats right up against the pitch, but they are painted in FC Basle's colours of bright red and blue. Countless football grounds have seats in club colours, but at Basle, because the particular colours are so strong, and the fans also wear red and blue, they seem to merge with the red and blue players to become a whole city overwhelming the visiting team. Herzog says: "It's very beautiful. And it was done with very little money. This is another typical aspect of football stadiums."
In fact, at Basle you feel even nearer the pitch than you do at Herzog's beloved English grounds. This is apparently because the green of the grass is a complementary colour to red and blue. Your eyes seize on it, and so it seems closer.
The stadium's exterior is quite original: during games it glows red and blue. "The idea is that the energy of the people, of the athletes, surges outwards," he explains. The Munich stadium will glow too.
However, Herzog and De Meuron don't have one trademark stadium. Their trademark is that their buildings don't have a trademark. In Munich, Herzog loves the curving walkway that takes fans to the ground. "This walk to reduce your distance to the stadium is very cinematographic," he says.
Beijing is different again: an Olympic stadium is a gathering place of all peoples, not a partisan venue. This one is being built of metal pylons reminiscent of the Eiffel tower - though the Chinese call it "the bird's nest" - and so, on ordinary days, people can hang around in nooks beneath and around the stadium. Herzog says the Chinese like hanging around in public.
Before he finishes with stadiums, he hopes to build one in England. It's the dream of an ageing outside- left. "I think if you don't have a passion for soccer you can't invent a stadium. You can do a stadium, because you can also do a cathedral if you aren't religious. But you couldn't come up with the idea."