Since its inauguration on 1 April 1989 by French President François Mitterrand, the Louvre Pyramid has become a Parisian monument in its own right. Although controversial in its early days, its glass and metal structure, designed by I. M. Pei, is an architectural achievement of the 20th century. Saint-Gobain Vitrages France patented a special glass, “Diamant”, which is used in the 673 panels of the pyramid. The technicians and engineers worked for four years to smooth out the surface of the glass roof as much as possible, by assembling and dismantling the structure.