Controversial from the start, IM Pei’s Grande Pyramide, in the Cour Napoléon at the Louvre, turns 20 this year.

French President François Mitterand commissioned the pyramid in 1981, as part of a Grand Projet, carried out in three phases. First, 45,000 square meters of underground space was created for storage and exhibition space (if you examine the pavement in the courtyard surrounding the pyramid, you’ll find large grates that open and close mechanically).

Then the streets and walkways were transformed to open the surrounding space visually and make the area more easily accessible to pedestrians. Finally, the glass and stainless pyramid was erected in the center of the courtyard.

Most agreed that the first two phases improved the Louvre’s function and accessibility. But the pyramid was often rejected on aesthetic grounds, saying that it was cold and inhuman in comparison to the adjacent classical wings.

The glass, which weighs 95 tons, was made by Saint-Gobain, manufacturer of the mirrors for the Hall of Mirrors, at Versailles.

The panes had to be completely transparent, so that looking through the pyramid would show the true colors of the surrounding Louvre wings. At the time, the only suitable glass was used for optics - the pyramid required that the glass be manufactured on an industrial scale.

The glass is held in place by lightweight aluminum mullions, anchored with handcrafted bolts, and sealed with silver silicone. When the pyramid was first constructed, it was cleaned by window washers who hung suspended by climbing ropes. Now, the windows are washed automatically.

If you go...

Musée du Louvre, 1st, Métro: Palais Royal - Musée du Louvre

Open daily except T, 9-6, until 10pm W/F

On the web: click here