How do you modernise the arch-modernist? This was the task facing the Dutch-born Rem Koolhaas when he won the competition to overhaul Mies van der Rohe's Illinois Institute of Technology. Nonie Niesewand hails his free-thinking, innovative solution
FOR the city that invented the skyscraper, the choice of Rem Koolhaas to build a new $25m campus centre at the Illinois Institute of Technology is surprising. A one-storey, rectangular building, wrapped in glass walls then covered by a contoured concrete roof, the centre will be surrounded by 18 beautifully proportioned, modular buildings by Mies van der Rohe, who designed and taught at the IIT architectural school, Crown Hall. Now this world-famous statement of modernism, a shrine to its maker, is - dare I say? - to be modernised by the 52-year- old Dutch-based Koolhaas, who won an international competition inviting 56 architects to design a new building on the campus. Thirty-nine responded and five were shortlisted. As commissions go, it's as challenging as asking Lucian Freud to paint over the Sistine Chapel.

Koolhaas admits that Mies dominates the campus but that "the buildings don't really look like Mies, it's almost factory ... accommodation, quite forbidding". Worse still, like all sixty-somethings, it's showing its age. "Quite tatty" in the words of John Zukowsky of the department of art and architecture at the Institute, who believes it was wartime scrimping and saving and the lack of skilled labour that affected its weathering. Hence the competition.

Mies is the mid-century modernist who invented that oft quoted definition of the movement, "less is more". The post-modernist Robert Venturi topped it with "less is a bore". So how will Koolhaas express the next -ism for the 21st century?

More or less subversively. The ground plan is the criss-crossing 60- year-old footpath carved by nomadic students trailing from the dormitories on the east to the lecture theatre on the west. In the intersections created by the trajectories, Rem Koolhaas plans oases that will house shops, offices, meeting rooms, dining rooms, sports facilities. As one competition juror, K Michael Hays, rather unfortunately put it: "Koolhaas has made a very permeable scheme that allows student activities to rub up against each other." All on one low level. Eventually, the project will include new housing, and an overhaul of the campus grounds.

Floating above in a stainless steel tube, 150 metres long, is the elevated railway, the El, as Chicagoans affectionately call it. Functionally, cladding it in a tube cuts the noise. Symbolically, it marks history moving on and leaving tracks. How the competitors dealt with the El was critical. Other practices shortlisted for the final phase of the competition were Peter Eisenmann of New York, Zaha Hadid of London, Helmut Jahn with Werner Sobek of Chicago and Stuttgart, and Kazuyo Sejima and Ryue Nishiza of Tokyo, "all with modernist affinities and future-oriented ambitions", as Rem describes them.

It's not the first time that Koolhaas has turned architecture on its side. Or head. Sometimes in his rapid-fire lectures - always over subscribed, with queues round the block - slides are screened upside down. "It doesn't matter," says Rem.

Take skyscrapers. The taller the building the thicker the base has to be to support it. But not for Koolhaas. With Ove Arup engineer Cecil Balmond, he configures 300m tower blocks supported by slender concrete columns. Sometimes the towers lean outwards, like the tower at Pisa. By clustering and intersecting them he can support lift shafts on wire sculptures and brace tower blocks on tailfins like space rockets. The effect is that of light refracting. Never a blank, glassy box.

This kind of free-thinking is why he won. Phyllis Lambert, a leading architectural curator, and a juror, confirmed the judges' unanimous choice of Rem Koolhaas. "You don't clone Mies. You can't clone Mies."

Though many adjectives - unswerving, seamless, a master at solutions of collision and intersection, tectonic, episodic, a pragmatist - used to describe Rem Koolhaas are true, listeners at his lectures are struck by the emotion and enthusiasm with which he expresses an idea. About three years ago he nearly closed OMA, his practice in Rotterdam, for lack of work. OMA stands for the Office for Metropolitan Architecture - "Sure it's a very pretentious title, after which any realisation may be found wanting," Rem says. But he persevered, and wrote SMLXL, an outsize book about scale in the sense of both mass and numbers, that wraps fairytales, anecdotes, jokes, dictionary definitions as well as subversive theories on structure, urban planning and clients into one volume.

Mediocre is a term of abuse he is unafraid of using, which is why his proposal for a revamp of the Museum of Modern Art in New York has heaped architectural hate mail on him. Rem began his proposal with a quote from Gertrude Stein that you can have a museum and that you can be modern but not in the same building.

In a new house he has designed in Bordeaux for a severely disabled client, a huge chunk of the house literally moves up via a vertical shaft through three floors. The middle floor, sandwiched between the cantilevered top floor and a modest ground floor dug into the rock, is all glass - slender, light and almost invisible. His quest to dismantle the gravity that still clings to the 20th century promises to give Rem Koolhass lift-off in the next.