At 9am this Saturday morning the doors of the Grand Palais in Paris will open on an exhibition of the art collection formed by the couturier Yves Saint Laurent and his business and civil partner Pierre Bergé. The doors close at midnight, as they will on Sunday (Monday’s view ends at 1pm), and during this three-day extravaganza some 30,000 visitors are expected to come to pay their respects to one of the most remarkable ensembles of fine and decorative arts created in the 20th century. From Monday evening, its dispersal begins.

The three-day, 733-lot auction, organised by Christie’s in association with Pierre Bergé & Associés, is expected to realise €200m-€300m (half the proceeds are to benefit scientific research in the fight against Aids). This is a sale that has it all: glamour, celebrity and, above all, objects of impeccable provenance, quality and rarity.

One suspects, however, that the glamour that surrounded this gilded couple, not to mention the multimillion price tags, may obscure the real genius of their achievement. For what the two men created over 30 years was that rare thing, a collection that is far more than the sum of its by no means inconsiderable parts.

When Christie’s came to catalogue the contents of the couple’s apartments in the Rue de Babylone and Rue Bonaparte, for instance, they ended up taking 10,000 photographs, recording every wall, every surface and every object. At first glance, these interiors seemed a brilliant synthesis of works of art of virtually every age and every medium. Only gradually did the prevailing rigour, intelligence and internal logic become clear. “I went into the Rue de Babylone apartment every day for three months and I always saw something new, and it was always fantastic,” muses the sale co-ordinator, the still incredulous Jonathan Rendell. “I have seen nothing like it in my 30 years in the auction business.”

Saint Laurent and Bergé met in 1958 but it was not until the early 1970s, when the couture business expanded into ready-to-wear, that they had the funds to begin to collect seriously. Two early influences prevail. The first was the Viscomte and Vicomtesse de Noailles. The iconoclastic Marie-Laure de Noailles’ recklessly eclectic yet grand salon mixed the spare minimalist interiors and furniture of Jean-Michel Frank with great Old Masters and Schatzkammer silver-gilt, souvenir postcards and the work of her avant-garde Surrealist protégés. “It was they who taught us to mix styles, eras and continents,” says Bergé.

The second influence was the couturier Jacques Doucet (1853-1929), the greatest collector of his day. After disposing of important holdings of 18th-century decorative arts (like Doucet, Yves Saint Laurent also used his art collections as inspiration for his designs), he turned to modern painting, acquiring the “Demoiselles d’Avignon”, for instance, directly from Picasso’s studio and commissioning sumptuous art deco furniture. It was the sale of his extraordinary furniture in 1972 that effectively launched the art deco revival, and Yves Saint Laurent and Pierre Bergé were among the buyers.

Here, for instance, they acquired the sumptuously exotic banquettes confected out of palmwood, red lacquer and leopard skin by Gustave Miklos (estimate €2m-€3m) and the African-inspired curule stool by Pierre Legrain (€400,000-€600,000) which, along with Eileen Gray’s remarkable “Dragons” armchair of 1917-1919 (€2m-€3m) and the pair of monumental Jean Dunand vases exhibited in the seminal Exposition Internationale des Arts Décoratifs in 1925 (€1m-€1.5m), rank among their most important art deco acquisitions. It is no coincidence that Giorgio de Chirico’s “Il Ritornante” (€7m-€10m) hung in exactly the same position high up on the wall in the Rue de Babylone apartment as it did in Doucet’s salon, or that where Doucet displayed the “Demoiselles”, the two collectors hung their own important cubist Picasso: “Instruments de musique sur un guéridon” (€25m-€30m).

After 1977, when YSL’s Opium was launched and became the world’s best-selling scent, it provided the pair’s acquisitions fund for paintings and sculpture. Stringent criteria were set: each piece had to come from a critical stage in the artist’s development, it had to be in pristine condition and it had to possess an exceptional, documented provenance. The first of many purchases made through the Parisian dealer Alain Tarica was Brancusi’s rough-hewn, totemic oak sculpture of the Parisian hostess Léonie Ricou, acquired from Léger’s widow for around $500,000 (€15m-€20m). The whole of Mondrian is summed up in three superlative works and their glorious Matisse, “Les coucous, tapis bleu et rose” of 1911 (€12m-€18m), which has never been lined or varnished, dates from that rare phase in the artist’s oeuvre when he moves on from fauvism to orientalism, the Spanish fabric depicted featuring in many subsequent works.

By the late 1980s, the pair had run out of wall space and so turned their attention to surfaces. Emulating once again Marie-Laure de Noailles, they began to acquire, from Kugel, a fabulous but hardly fashionable princely collection of 16th-18th-century German silver, silver-gilt and gold: Wunderkammer pieces such as exotic mounted nautilus shells and ostrich eggs but also a magnificent group of huge standing cups, drinking cups and gold boxes. There are renaissance bronzes and enamels, like the late-16th-century parcel-gilt grisaille enamel platter attributed to Jean de Court (€300,000-€400,000), plus exceptional cameos and mounted cups in every conceivable semi-precious hardstone.

It is tempting to attribute this penchant for the sumptuous, tactile and exotic to Saint Laurent, along with the apartment’s sense of structure, colour (or lack of it) and, at times, theatrical, crepuscular, even seductive mood. From the well-read, cultivated Bergé came a literary and historical sensibility; objects such as Duchamp’s Dada scent-bottle coffin (€1m-€1.5m). But it seems that in their acquisitiveness, both men were equal, and passionate, partners. Even after Bergé moved to the Rue Bonaparte at the end of the 1980s, collecting, and the collection, continued to bind them. They had developed their own eye, and found one very individual voice.

What is clear is that there was never any sense of hierarchy in their collecting; every object, major or relatively minor, was there to add its own particular magic, and resonance, to the grander scheme. They were not in pursuit of trophies per se; rather, gathering pieces of a visual, intellectual and emotional jigsaw evoking that heroic age of early-20th-century French culture and creativity. What they confected was, in a sense, Proust’s madeleine. And Proust was an author Saint Laurent particularly admired.

The catalogue (€200) is also available online at www.christies.com