PARIS — Louis XIV waged architecture as he waged war — with total commitment, huge resources and soldiers from his army — and his greatest architectural campaign was, of course, Versailles, the sprawling baroque palace he wrapped around his father’s original hunting chateau outside Paris. When his army wasn’t at war, he enlisted soldiers to help build the palace, moving in with his court in 1682.

The king who famously declared that he was the state might have added, “Versailles, c’est moi.” Versailles was a monument that conflated the state and the king in the same architectural glory, majestic avenues radiating into the landscape as though emanating from the Sun King himself. Versailles, with the king at its center, organized the country.

Through five Republics, the French have assiduously cared for this apogee of French culture, a national symbol baked into the country’s psyche. Touching any part of Versailles is like performing brain surgery on France: a very delicate matter.

But Versailles was meant to receive a few people well, arriving in the Royal Courtyard by carriage, not 7.5 million visitors a year coming on foot with backpacks to check. With the notable exception of 1789, crowd control was never an issue. In recent years, temporary structures were erected in the courtyard for frisking visitors and issuing tickets before sending them toward a messy warren of entrances. What the museum needed was the equivalent of the Pyramid at the Louvre, a foyer to absorb crowds with grace and efficiency.

In 2011, the archmodernist Parisian architect Dominique Perrault won a closed competition to transform the Pavillon Dufour and the attached Old Wing flanking the Royal Courtyard into a proper reception hall. Mr. Perrault — perhaps best known for his National Library of France in Paris on the Seine, centered on a sunken garden — won, in a sense, by acupuncture.

By creating a 3,000-square-foot basement for a gift shop, coat check and bathrooms beneath the Pavillon and the adjacent Princes’ Courtyard, he created a new loop through the chateau. Visitors could enter the palace through the Pavillon, proceed on the circuit and finish in the basement, where a grand staircase would take them back up to the Courtyard. From there, they could visit the gardens and park, or head out of the palace.

“The main question of the program was the entrance and the exit,” said Mr. Perrault, a 63-year-old Parisian. “The second was developing the restaurants and auditorium on the second and third floors, and making sure that all the parts, the global function of the Pavillon, worked together.”

Louis XIV would have understood: The proposal was pure strategy, a small pinprick, to make sense out of the visit. The excavated basement, illuminated by an expanded wall of glass, elegant and minimal, added much-needed room to a huge museum that, paradoxically, lacked space for visitors who were never anticipated.

“The goal was to increase the square footage without adding any visible building,” he said. “The strategy was to go into the ground.”

Mr. Perrault is simply the most recent architect to add a stone to Versailles. The whole history of the chateau is a case of nested Russian dolls: Louis XIV’s architect, Louis le Vau, famously enlarged the small original chateau, to which architects over two centuries added wings, the chapel, the theater, annexes and outbuildings, including the Grand Trianon, set within its own park, and the Petit Trianon, completed in 1768 during the reign of Louis XV and given to Marie-Antoinette by Louis XVI.

In a building designed for the French court, each successive architect proved courtly, proceeding by diplomatic agreement, though styles shifted from late Renaissance to Baroque to neo-Classical. The tradition at Versailles, however, was not to imitate the previous architect. Though the chateau now seems the epitome of classical tradition, it emerged as a progressive collage of inventions representing the most advanced thinking of its time.

The scale of the enterprise was so vast, the Brasília of its day, that Louis XIV hired André Le Nôtre to design the landscape on the king’s back 40 and Charles Le Brun to create the elaborate interiors.

“The chateau in itself is not very big or very high, as at the Hermitage in St. Petersburg,” Mr. Perrault said. “What’s impressive is the opposition of the two huge scales: the city with its urban aspect, and the landscape in all its immensity.”

The Perrault Staircase, which Mr. Perrault calls a hyphen between centuries. Credit Patrick Tourneboeuf/Tendance Floue and OPPIC

Mr. Perrault is the first Modernist to make a major contribution, and as a Modernist, he tends toward Minimalism: straight lines, lots of glass, dematerialized form, transparency, reflections, ephemeral effects, more with less. He resolved, bravely, “to bring the present inside,” knowing he faced the guillotine of public opinion for any undiplomatic moves.

The exteriors were a literal restoration executed under the supervision of the Head Architect for Historic Monuments at Versailles. Mr. Perrault’s task, the reorganization and design of the interiors, was less straightforward. Styles were already mixed. The neo-Classical Pavillon, by Ange-Jacques Gabriel, was added to the baroque Old Wing by le Vau, which was later modified by Jules Hardouin-Mansart. As a Modernist, Mr. Perrault faced a daunting architectural gang populated by the most famous classicists of French architectural history. Adding to the mix was a structural reconstruction in reinforced concrete done in the 1920s that had destroyed much of the interior (though some of the original paneled rooms remained).

Mr. Perrault restored what survived the reconstruction — paneled rooms on the upper floors that will be a restaurant complex run by the chef Alain Ducasse — then opened up spaces below by removing walls, leaving the perimeters plain and bare. He stripped interiors to the shell to achieve clarity, as though cleansing the palate.

Visitors now enter through Gabriel’s portals, under an entablature that reads “To the Glories of France,” into meticulously detailed classicized limestone vestibules. They step into a large, open reception and ticketing hall where broad lines paved in brass cross the floor, indicating where bearing walls had been.

In his lavish interiors, Le Brun made tangible in furniture and decoration larger architectural ideas: foliage depicted in rugs and gilded sconces all scroll with the same baroque energy as the marble staircases. Mr. Perrault created new chandeliers and sconces with industrial materials. The metals, including bronze, seem to tinge the light warmly.

Louis XIV was fascinated by parabolic reflectors, concave mirrors that reflect and intensify the sun. Mr. Perrault’s art director, Gaëlle Lauriot-Prévost, created “solar” sconces that scatter light in all directions. The designers draped wire mesh across the ceilings, swooping down the length of the hall. They took the famous Versailles parquet floor pattern, a basket weave inset within a larger diagonal grid, and reinterpreted wood in bronze.

For many Modernists, decoration is criminal, but Mr. Perrault respected the decorative arts tradition of Versailles and translated figurative forms into abstractions that highlight shape, material and light itself. What remains classical in his approach is his strict respect for symmetry.

In this reception chamber, between the two courtyards, he subtly refers to the gilded Hall of Mirrors. In that great front gallery of the chateau overlooking the gardens, the long back wall of mirrors reflects the views through the windows opposite. Here, Mr. Perrault let the windows on either side of the room mirror each other while acting as picture windows.

Mr. Perrault’s hall of mirrors has no mirrors. His statement is understatement. The Minimalist is offering a void in one of the most decoratively saturated palaces on earth.

“The idea is that as soon as you step through the main entrance into the first room, you’re in the chateau, in the house. You’re a guest,” he said.

He chuckled over an unexpected honor: that wide, sweeping marble staircase that he designed to join the basement to the Princes’ Courtyard? He calls it a hyphen between centuries. Everyone else refers to it as the Perrault Staircase.

Contrary to what Shelley wrote about how great works of potentates vanish into the sands of time, the glory embedded in this chateau’s celestial frescoes and majestic suites has endured — and the small, select club of Versailles architects has admitted a new member.