not interchangeable with other instruments. Classical period Christoph Willibald Gluck was the first major composer to use the trombone in an opera overture, Alceste (1767), but he also used it in operas such as Orfeo ed Euridice, Iphigénie en Tauride (1779) and Echo et Narcisse. The construction of the trombone changed relatively little between the Baroque and Classical period. The most obvious change was in the bell, slightly more flared. The first use of the trombone as an independent instrument in a symphony was in the Symphony in E♭ (1807) by Swedish composer Joachim Nicolas Eggert. But the composer usually credited with the trombone's introduction into the symphony orchestra was Ludwig van Beethoven in Symphony No. 5 in C minor (1808). Beethoven also used trombones in his Symphony No. 6 in F major ("Pastoral") and Symphony No. 9 ("Choral"). Romantic period 19th-century orchestras Trombones were often included in compositions, operas, and symphonies by composers such as Felix Mendelssohn, Hector Berlioz, Franz Berwald, Charles Gounod, Franz Liszt, Gioacchino Rossini, Franz Schubert, Robert Schumann, Giuseppe Verdi, and Richard Wagner among others. Although the trombone trio had been paired with one or two cornets during the Renaissance and early Baroque periods, the disappearance of the cornet as a partner and replacement by oboe and clarinet left unchanged the trombone's purpose: to support the alto, tenor, and bass voices of the chorus (usually in ecclesiastical settings) where harmonic moving lines were more difficult to pick out than the melodic soprano line. But the introduction of trombones into the orchestra allied them more closely with trumpets, and soon an additional tenor trombone replaced alto. The Germans and Austrians kept alto trombone somewhat longer than the French, who preferred a section of three tenor trombones until after the Second World War. In other countries, the trio of two tenor trombones and one bass became standard by about the mid 19th century. Trombonists were employed less by court orchestras and cathedrals and so were expected to provide their own instrument. Military musicians were provided with instruments, and instruments like the long F or E♭ bass trombone remained in military use until around the First World War. But orchestral musicians adopted the tenor trombone, the most versatile trombone that could play in the ranges of any of the three trombone parts that typically appeared in orchestral scores. Valve trombones in the mid-19th century did little to alter the