The Kunstbibliothek is one of the most exhaustive art libraries in Europe, and the Kupferstichkabinett one of the most interesting museums of graphic art. Begun during the reign of Frederick William, the collection comprises more than a million drawings, water colours, gouaches and pastels from the 14C to the 20C, and almost 540,000 engravings from the late Middle Ages to the present day. The collection of drawings by old German and Dutch Masters – including 80 by Rembrandt – is unique in the world.