Olivier Eugène Prosper Charles Messiaen was a French composer, organist, and ornithologist. One of the major composers of the 20th century, he was also an outstanding teacher of composition and musical analysis. Messiaen entered the Conservatoire de Paris at age 11 and studied with Paul Dukas, Maurice Emmanuel, Charles-Marie Widor and Marcel Dupré, among others. He was appointed organist at the Église de la Sainte-Trinité, Paris, in 1931, a post he held for 61 years, until his death. He taught at the Schola Cantorum de Paris during the 1930s. After the fall of France in 1940, Messiaen was interned for nine months in the German prisoner of war camp Stalag VIII-A, where he composed his Quatuor pour la fin du temps for the four instruments available in the prison—piano, violin, cello and clarinet. The piece was first performed by Messiaen and fellow prisoners for an audience of inmates and prison guards. Soon after his release in 1941, Messiaen was appointed professor of harmony at the Paris Conservatoire. In 1966, he was appointed professor of composition there, and he held both positions until retiring in 1978.