was particularly urged by the architectural theorist and historian Eugène Viollet-le-Duc. In his 1872 book Entretiens sur L'Architecture, he urged: "use the means and knowledge given to us by our times, without the intervening traditions which are no longer viable today, and in that way we can inaugurate a new architecture. For each function its material; for each material its form and its ornament." This book influenced a generation of architects, including Louis Sullivan, Victor Horta, Hector Guimard, and Antoni Gaudí. Early modernism in Europe (1900–1914) At the end of the 19th century, a few architects began to challenge the traditional Beaux Arts and Neoclassical styles that dominated architecture in Europe and the United States. The Glasgow School of Art (1896–99) designed by Charles Rennie Mackintosh, had a façade dominated by large vertical bays of windows. The Art Nouveau style was launched in the 1890s by Victor Horta in Belgium and Hector Guimard in France; it introduced new styles of decoration, based on vegetal and floral forms. In Barcelona, Antonio Gaudi conceived architecture as a form of sculpture; the façade of the Casa Battlo in Barcelona (1904–1907) had no straight lines; it was encrusted with colorful mosaics of stone and ceramic tiles. Architects also began to experiment with new materials and techniques, which gave them greater freedom to create new forms. In 1903–1904 in Paris Auguste Perret and Henri Sauvage began to use reinforced concrete, previously only used for industrial structures, to build apartment buildings. Reinforced concrete, which could be molded into any shape, and which could create enormous spaces without the need of supporting pillars, replaced stone and brick as the primary material for modernist architects. The first concrete apartment buildings by Perret and Sauvage were covered with ceramic tiles, but in 1905 Perret built the first concrete parking garage on 51 rue de Ponthieu in Paris; here the concrete was left bare, and the space between the concrete was filled with glass windows. Henri Sauvage added another construction innovation in an apartment building on Rue Vavin in Paris (1912–1914); the reinforced concrete building was in steps, with each floor set back from the floor below, creating a series of terraces. Between 1910 and 1913, Auguste Perret built the Théâtre des Champs-Élysées, a masterpiece of reinforced concrete construction, with Art Deco sculptural bas-reliefs on the facade by Antoine Bourdelle. Because of the concrete construction, no columns blocked the spectator's