G minor has been considered the key through which Wolfgang Amadeus Mozart best expressed sadness and tragedy, and many of his minor key works are in G minor, such as the Piano Quartet No. 1 and the String Quintet in G minor. Though Mozart touched on various minor keys in his symphonies, G minor is the only minor key he used as a main key for his numbered symphonies (No. 25, and the famous No. 40). In the Classical period, symphonies in G minor almost always used four horns, two in G and two in B♭ alto. Another convention of G minor symphonies observed in Mozart's No. 25 was the choice of E-flat major, the subdominant of the relative major Bb, for the slow movement, with other examples including Haydn's No. 39 and Johann Baptist Wanhal's G-minor symphony from before 1771.