Although the 19th century was the greatest period of the waltz, people continued to write and dance waltzes in the 20th century. In his opera "Der Rosenkavalier" (1909) the German composer Richard Strauss (no relation of Johann Strauss) the story is about Vienna in the old days, and so he uses the waltz to create the feeling of a time that was past. The waltz continued to be used in a lot of operettas, e.g. by Franz Léhar in "The Merry Widow ". The French composer Maurice Ravel wrote waltzes, including a brilliant piece for orchestra which was simply called "La Valse". Like Richard Strauss in "Der Rosenkavalier", Ravel was trying to describe the music of a century ago. "La Valse" is a piece which lasts about 20 minutes in one continuous movement. Lots of different instruments have a share in playing many different tunes.