By Querfurt, the ducal Saxe-Weissenfels line gained the status of an Imperial State (at times called Saxe-Querfurt) and member of the Upper Saxon Circle, though without a vote in the Reichstag. In 1659 Augustus also acquired the County of Barby, which upon his death in 1680 was granted to his younger son Heinrich. He built the new baroque castle at Barby from 1687. Augustus eldest son and successor Duke Johann Adolf I sold Burg to Brandenburg in 1687.
George Frideric Handel's father Georg Händel from 1657 on served as a physician to Duke Augustus of Saxe-Weissenfels, the composer himself was born in the former ducal residence of Halle. According to legend it was Duke Johan Adolf I admiring George Frederic's performance on the church organ of Neu-Augustusburg Castle, who promoted his musical career. In 1713 Johann Sebastian Bach dedicated his cantata Was mir behagt, ist nur die muntre Jagd, BWV 208 to Christian of Saxe-Weissenfels in celebration of the duke's 31st birthday, it was first performed at the ducal Neuenburg Castle at Freyburg.