offers courses in most major world languages to all the students. Additional centres of research and laboratories gravitate around the departments, which function as nodes of research. The emphasis is placed squarely on interdisciplinarity and students who entered from a scientific concours (thus having mainly studied in their preparatory school maths, physics and chemistry or biology) are encouraged to attend courses in the literary departments. Conversely, maths and physics introductory courses are on offer for the students from the "literary" departments. The school's diploma, instituted in 2006, requires students to attend a certain number of courses not related to their major. Libraries The École normale supérieure has a network, known as Rubens, of ten libraries shared out over its sites, which taken together make up the third largest library in France. The catalogue is available for consultation online. Entrance to the libraries is reserved to domestic and international researchers of doctoral level, as well as to the teachers at the school, normaliens, other ENS students, and PSL Research University students. The main library, devoted to literature, classics, and human sciences, dates back to the nineteenth century when it was greatly expanded by its director, the famous dreyfusard Lucien Herr. Its main reading room is protected as a monument historique. This main library, which covers several thousand square metres, is one of the largest free access funds of books in France, with upwards of 800,000 books readily available and more than 1600 periodicals. Its classics section is part of the national network of specialised libraries (Cadist). A secondary library concerned with social science, economics, and law is located at the Jourdan campus for social science. This library has more than 150,000 books in the subjects it covers. The school also has specialised libraries in archeology, cognitive sciences, mathematics and computer science, theoretical physics. A recently unified natural sciences library was opened in 2013, aiming to bring together in a central place on rue d'Ulm the libraries of physics, chemistry, biology and geoscience.ENSSIB – French record of new libraries The school also features two specialised centres for documentation, the Bibliothèque des Archives Husserl, and the Centre d'Archives de Philosophie, d'Histoire et d'Edition des Sciences. Affiliations Two other écoles normales supérieures were established in the 20th century: the École Normale Supérieure de Lyon (sciences and humanities); and the École normale supérieure Paris-Saclay (pure and applied sciences, sociology, economics and management, English language). More