A few weeks ago they made a visit to Berlin to oversee the progress of the project, and we arranged to meet. They had a packed schedule: a book-signing session in central Berlin, a conference at which Christo addressed a collection of local architects and other professionals on the history of the project, and, late in the afternoon, a reception party at his grand offices opposite the Reichstag.
The scene would be familiar to anyone who has attended artists' launch parties: expensively suited men strode around the rooms sizing up the works - sketches and drawings of the Reichstag in its future glory, complete with Christo and Jeanne-Claude's ma n tle of silvery cloth - and expensively frocked women imagining the pictures on their dining room walls. Purchases were being made. A small drawing measuring 8.5 by 11 inches was sold to a woman for $9,000, while a distinguished looking gent was flourishi ng his cheque book for a larger sum (prices rise to $220,000 for a work measuring eight feet by four).
Along the corridors were photographs and drawings of many earlier projects: the Valley Curtain in Colorado (1972), the Surrounded Islands in Miami (1983), the Wrapped Pont Neuf (1985), the Blue Umbrellas in Japan (1991). Each of these took some years to achieve, but never quite so long as this.
As the crowd thinned out, Christo and Jeanne-Claude led me to a quieter room, asked for scotch and soda, and began to explain their extraordinary devotion to this project. It began with a postcard from Michael Cullen, an Englishman living in Berlin, showing the building. It had held Germany's parliament, been burnt down by Hitler, and damaged in the war; it was restored in the 1960s, but then sat, virtually disused, right next to the Berlin Wall.
Didn't the Reichstag's change of fortunes put them off the idea? "The building has not changed," Christo replied in a gentle French-Balkan lilt. "It has an additional dimension. Everything that happened before 1990 will still belong to the building." "All that stays," interjected Jeanne-Claude. (They have the old couple's habit of completing one another's sentences: born on the same day, June 13, 1935, they met in Paris in 1958 and have been inseparable ever since).
"When people walk around it," says Christo, "it will be like a living object. They will question everything they know about the Reichstag; not just the aesthetics, but how the building will be used, what kind of politics will be made in five years time. That is really a dynamic situation."
This philosophy underlies all of the Christos' work: transform the outward appearance of a landscape or object, and the viewer is moved to reconsider its inner qualities.The familiar is given new energy through its unfamiliar clothes.
It was an ideal time to meet the pair. Their long-fought battle to convince the German parliament of the project's validity is over (a full session of the Bundestag debated the issue last February, and they won a narrow victory after some stirring speeches on both sides); the physical process of manufacturing and coating the fabric and the rope is well in hand (a third of the 60 panels are complete, and a technique of "vacuum chamber vaporisation" has been discovered to add a minute coating of aluminiumto it); Christo's drawings are selling well - he will make a brief visit to London in March for the opening of an exhibition - and his regular team of engineers and project managers are all in harness.
There are so may diverse stages to the work that the Christos do not have a typical working day. They will scout a location for months before deciding on it. Then begins the task of winning over the local authorities, landowners and planners. In the mea n time, when they have some days back at home in their five-storey converted SoHo warehouse, Christo sets to work drawing and modelling in his studio, while Jeanne-Claude receives potential buyers and co-ordinates other aspects of each project. They are,i n a way, curiously detached from the physical labour of the eventual work. Christo will even describe framing his own drawings as a "relaxation".
The only typical aspect of the day we met was their utter concentration on the work in hand. "I am a workaholic, Jeanne-Claude also," said Christo, with the most enchanting half-smile. "We never have holidays. But all our projects are so richly different. That is probably very invigorating." Even the Reichstag, with rejections following one after another in 1977, 1981 and 1987, was a source of energy and the occasion of some wonderful friendships: "Willy Brandt climbed the 90 steps to our studio in 1980to ask us not to abandon the Reichstag project. He was very influential to keep the project alive."
For the project manager, Wolfgang Volz, there is a similar variety of tasks, although he is more firmly grounded in Berlin. With his engineers he will inspect the building from top to toe, deciding how each sheet of fabric will be anchored, how the team of climbers will exit through the roof and abseil down the facade as the fabric unrolls. Volz and his wife Sylvia are photographers, and will take more pictures of the unwrapped building, besides preparing for the vital pictures during the two weeks from23rd June, when it will be wrapped.
All plans are being made towards this deadline: Christo must press on with more drawings, and between them he and Jeanne-Claude must sell enough to raise the £10m cost of the project, or else agree a bank loan. The German operation must ensure the materials, staff and machinery - such as the crane, which will winch the material up on to the Reichstag - are in place.
Any delay could be fatal. Sir Norman Foster is due to begin a complete reconstruction of the building later next summer, before it becomes Germany's seat of government again in 1998.
After the building's unwrapping, the Christos will move on. They have three more projects officially "in progress'': one in Abu Dhabi which originated in 1979, another for New York's Central Park, called The Gates (begun in 1980), and a further plan to suspend a 10 or 12km ribbon of coloured fabric over a river in the Rockies. This only occurred to them in 1992, and is their current favourite.
Meanwhile, the progress of Wrapped Reichstag inches towards its conclusion.
Like the pursuit of a male bee for its queen, which ends in triumph followed immediately by death, the Christos pursue their two weeks of consummation. You can feel the adrenalin beginning to course through their collective, inseparable bodies as the ticking clock grows louder.