comprehensive catalog of the library's holdings. The Athenaeum's exhibition area opened up when the Museum of Fine Arts moved the collections into their own space overlooking Copley Square. Cutter took advantage of the space, using it to spread out the collections and to revise and complete the five-volume catalog. He created his own classification system, known as Expansive Classification, in order to revise and finish the five-volume catalog. Later, the Cutter system became the basis for the Library of Congress classification system; the sections of call number used to alphabetically designate authors’ names are still known as "Cutter numbers" in the Library of Congress system. Establishment of Museum of Fine Arts Many of the Trustees at the Boston Athenaeum participated in the movement to create a separate museum in Boston. In the years 1872–1876, Boston's Museum of Fine Arts exhibited in the Athenaeum's gallery space while waiting for construction of its building to be complete. There would be no more annual exhibitions; shelves were installed and the library spread to the first and third floors. 20th and 21st centuries From 1913–1914, the Boston Athenaeum employed the architectural firm of Bigelow and Wadsworth to expand the building. The fourth and fifth floors were set back so as not to disrupt the symmetry of the façade. This renovation fireproofed the building and expanded the space, including the addition of the beautiful fifth floor reading room and the fourth floor Trustees’ Room. At the same time, much-needed shelving was installed in the form of a drum stack — a ten-story Snead stack occupying a semi-circular space from the basement to the third floor. The Boston Athenaeum was declared a National Historic Landmark in 1966. Between 1999 and 2002, the Boston Athenaeum underwent a major renovation to update its climate control system, gain more space for books, and add new gallery space on the first floor. In May 2020, Leah Rosovsky was appointed as Stanford Calderwood Director of the Athenaeum. Gilbert Stuart portraits The Athenæum had long owned two famous, unfinished portraits of George and Martha Washington. They had been on loan to the Boston Museum of Fine Art since 1876, but eventually the Athenæum, needing money, asked the Museum to purchase them outright, which the Museum declined to do. The Athenæum then agreed to sell the portraits to the National Portrait Gallery (an arm of the Smithsonian Institution in Washington, D.C.) for $5