Johann Joseph Fux, teacher of Caldara in 1716, Zelenka and Quantz in 1717, and imperial court composer in Vienna from 1715, is better known today as the author of Gradus ad Parnassum (1725), a treatise on sixteenth-century counterpoint in the style of Palestrina. In 1745 Gradus was translated into German by Bach's pupil Lorenz Christoph Mizler. Bach is known to have owned a copy of Gradus in its original Latin version. Fux is mentioned in a letter (1775) from Carl Philip Emanuel to Forkel as one whose works his father had especially valued in his later years. Of Fux's eighteen operas, "Elisa" (Vienna 1719) and "Costanza e Fortezza" (Prague 1723) are the more well known. In addition Fux wrote Masses (incl. Missa canonica), Psalms, Requiems, and instrumental works.