Art Nouveau is a style of art, architecture, and applied art from throughout the world, with a focus on the decorative arts. It’s also known as the Modern Style in English. During the Belle Époque period, which ended with the outbreak of World War I in 1914, the style was most dominant between 1890 and 1910. It was a reaction against 19th century architecture and decoration’s academic art, eclecticism, and historicism. Natural shapes such as the sinuous curves of plants and flowers were frequently used as inspiration. A concept of vitality and movement, often portrayed by imbalance or whiplash lines, was also a signature of Art Nouveau, as was the use of new materials, notably iron, glass, ceramics, and later concrete, to produce unique shapes and greater open spaces.

Examples:

The Paris Universal Exposition (1900)

The Paris Universal Exposition of 1900 was the peak of Art Nouveau in Paris, bringing together several of the style’s remarkable artists and designers and introducing the style to the Exposition’s forty-eight million visitors. The interiors of the mainly two pavilions of fine arts, the Grand Palais and the Petit Palais, featured Art Nouveau architecture. It was also seen in the Palace of Decorative Arts, which included pieces by Louis Majorelle, René Lalique, Daum, and other French designers. Hector Guimard created the Art Nouveau edicules for the platforms for the Paris Métro, which was constructed shortly after the Exposition opened.

The first line was shown without ceremony on July 19, 1900, during the World’s Fair (Exposition Universelle).  The system grew rapidly until World War I, and by the 1920s, the centre had been completed; expansions into the suburbs were constructed in the 1930s. https://en.wikipedia.org/wiki/Paris_Métro#/media/File:Metra_in_Paris_(1105185529).jpg

---

Sources: https://en.wikipedia.org/wiki/Paris_Métro , https://www.metmuseum.org/toah/hd/artn/hd_artn.htm ,