Despite increasing deafness Beethoven was responsible for a prodigious output: nine symphonies, thirty-two piano sonatas, sixteen string quartets, the opera Fidelio (1814), and the Mass in D （the Missa Solemnis, 1823）. In his Ninth Symphony (1824) he broke with precedent in the finale by introducing voices to sing Schiller's Ode to Joy. He is often seen as bridging the classical and romantic movements.