The Museum collections feature historical artifacts from the recovered treasures of the Wawel Cathedral, the Royal Castle and other objects donated by Polish noble families ("szlachta"). Izabela also bought the treasures of the Duke of Brabant, including his books which were considered a particular highlight of the collection. Influenced by the Romantic artistic movement, she also acquired objects of sentimental significance that represented the glory and misery of human life. Among these were Shakespeare's chair, fragments from the alleged graves of Romeo and Juliet in Verona, ashes of El Cid and Ximena from the Cathedral of Burgos, and relics of Abelard and Heloise, and Petrarch and his Laura. The library's book collection was later enhanced with Tadeusz Czacki's collection, which included archives of Stanisław August Poniatowski, last king of Poland.