In the 20th century, French-Swiss architect Le Corbusier designed several buildings in France. More recently, French architects have combined both modern and old architectural styles. The Louvre Pyramid is an example of modern architecture added to an older building. The most difficult buildings to integrate within French cities are skyscrapers, as they are visible from afar. For instance, in Paris, since 1977, new buildings had to be under . France's largest financial district is La Défense, where a significant number of skyscrapers are located. Other massive buildings that are a challenge to integrate into their environment are large bridges; an example of the way this has been done is the Millau Viaduct. Some famous modern French architects include Jean Nouvel, Dominique Perrault, Christian de Portzamparc or Paul Andreu.