The first metro line was opened in Paris on the occasion of the World Fair in Paris in 1900. Hector Guimard designed the first metro stations, using the formal language of Art Nouveau. He used industrial materials such as iron and glass to create filigree and transparent structures reminiscent of buds, stems and leaves. The cast-iron grids, which were located at almost all station entrances, are decorated with a vegetal designed shield. In the lower area, the curved, interwoven lines form a letter. The capital "M" stands for "Métro". You can still find traces of Guimard's design at 66 stations in Paris.