Altering the Louvre architecturally is tantamount to operating on the collective French psyche. The former palace embodies much of the French history that every schoolchild learns by rote: Changing it means tampering with inculcated cultural memory. The monumental glass pyramid that I.M. Pei famously built in 1989 in the Cour d’Honneur—among the first changes that former President François Mitterrand initiated for the “Grand Louvre” museum expansion project—polarized the French, eliciting cris de coeur on both sides of the controversy. Some still don’t accept it.

Twenty-three years later, the Louvre has just opened the last major alteration in Mitterrand’s “Grand Louvre” plan: the new wing of the Department of Islamic Art. Winning an international competition in 2005, Italian architect Mario Bellini and French architect Rudy Ricciotti designed a glass-walled pavilion with an undulating roof of metal mesh centered in the 18th-century Cour Visconti. The courtyard, a hallowed precinct of serene classical façades, was the Louvre’s last available building site.

Since the September opening of the $130 million addition, controversy has been conspicuous by its absence. The new structure has been accepted and even praised in the general press, without any notable resistance.

In his inaugural comments, the director of the Louvre, Henri Loyrette, noted that the new addition follows in the Louvre’s own tradition of architectural innovation: Though France’s strict architectural preservation laws give the impression that the country has been architecturally conservative, Loyrette suggests that, to the contrary, the kings and subsequent heads of state were architecturally progressive and always hired the best and brightest of their time to work on the Louvre.

The result is a monument that constitutes a nearly encyclopedic history of official national architecture, from its original medieval origins through its renaissance, baroque, and Napoleonic incarnations.

Like Pei’s glass pyramid, the new structure is basically a glazed space frame, composed of some 8,800 metal tubes, which support a sandwich of wire-mesh scrims that filter and evenly distribute natural light. But if Pei’s pyramid, as a Euclidean form that shows off the mechanics of structural support, adheres to a 20th-century mechanical paradigm, Bellini and Ricciotti’s design belongs instead to a digital design paradigm of the 21st century. Resembling a wafting handkerchief or flying carpet or Bedouin tent, the undulating roof has the iridescence of a dragonfly wing. Flat planes have been warped by computational splines into a floating shell of complex curves. Linear has gone nonlinear.

Visitors peering out classical windows into the majestic Cour Visconti on the Seine side of the palace see the pavilion’s roof below, a Saharan topography of gold-tinted mesh dunes. The roof rises and falls in the courtyard without touching the sacrosanct walls or interrupting the view of the façades. The courtyard has gained an unexpected, post-classical geometry that is much kinder and gentler than Pei’s more imposing and competitive pyramid. With a keen sensitivity to the existing architecture, the addition has added a chapter on parametric design to the Louvre’s eminent history.

The choice of the winning design, in fact, rested on its perceived respect for the Cour Visconti: Bellini and Ricciotti’s design was the only entry to build down into the ground beneath the courtyard, rather than up. The architects proposed that the visible part of the pavilion be built at grade with the roof rising only to the lower level of the piano nobile, but they also excavated 12 meters into the court for a subterranean gallery that linked laterally into other existing basement galleries. They added another subterranean level below as a service floor.

Excavating below grade required the pharaonic and costly effort of shoring up and underpinning the palace’s existing foundations, but the basement galleries promised the curatorial advantage of connecting the Islamic collections to other thematically related collections, giving added cultural dimension to the displays. Exhibitions of Islamic objects will now complement adjacent galleries of Byzantine art from the Eastern Mediterranean.