in the second half of the eighteenth century in germany, the sonatas were transmitted through hand copies made by bach's pupils and circle from leipzig. during that period berlin rose to prominence as the centre of musical activities in germany. the court of frederick the great, where carl philipp emanuel bach was appointed harpsichordist in 1740, had a number of exceptional violinists, including johann gottlieb graun, the violin teacher of wilhelm friedemann bach, and franz benda, another of graun's pupils. in berlin princess anna amalia, the sister of frederick the great, was a keen amateur keyboard player and from 1758 had bach's pupil johann kirnberger as her music teacher: since 1751 he had been employed as another of frederick's court violinists. anna amalia's music library—the amalienbibliothek, now incorporated in the berlin state library—contained a large collection of bach manuscripts, including a hand copy of the sonatas. many musical compositions from her collection were transmitted to vienna by baron van swieten, the austrian ambassador to berlin: starting in the 1770s, van swieten ran his only weekly salon in vienna devoted to the music of bach. bach's music was also performed in berlin outside the royal court. the family of daniel itzig, banker to frederick the great and his father, provided a cultural milieu for musical connoisseurs: four of his daughters, sara, zippora, fanny and bella (maternal grandmother of felix mendelssohn), were all keyboard players.