Following work by Mansart (1645), Robert de Cotte extended the library by adding two galleries in the 18C. With its metallic architecture characteristic of the Second Empire, the printed book reading room is the work of Labrouste (1854). The Mazarin gallery by Mansart is to become a museum in 2020. Since 1998 and the transfer of books and periodicals to the Tolbiac site, the building has housed manuscripts, prints, photos, maps, plans and music scores. It is also home to the Musée des Monnaies, Médailles et Antiques.