An encore is an additional performance given by performers after the planned show has ended, usually in response to extended applause from the audience. Multiple encores are not uncommon, and they initially originated spontaneously, when audiences continued to applaud and demand additional performance from the artists after they had left the stage. However, in modern times they are rarely spontaneous and are usually a pre-planned part of the show. Instrumental concerts At the end of a concert, if there is prolonged applause, one more relatively short piece may be performed as an encore. In some modern circumstances, encores have come to be expected, and artists often plan their encores. Traditionally, in a concert that has a printed set list for the audience, encores are not listed, even when they are planned. A well-known example is the performance of the Radetzky March and The Blue Danube at the end of the Vienna New Year's Concert by the Vienna Philharmonic Orchestra; neither piece is ever listed in the official program, but they are traditionally played every year. Opera performances Beginning in the 18th century, if an aria was strongly applauded, it might be repeated. For example, at the premiere of Mozart's Marriage of Figaro, 1 May 1786, and other early performances, "many pieces were encored, almost doubling the length of each performance". Restrictions on encores For "Figaro", on 9 May 1786 Emperor Joseph II of Austria issued an order limiting encores. By tradition, some world-class opera houses, such as La Scala and the Metropolitan Opera, officially discourage encores, especially for vocal solos, as encores were associated with less serious performances. In the mid-19th century, encores were officially banned in northern Italy, since the Austrian-Italian authorities felt they would lead to public disorder. In 1921, encores were forbidden at la Scala (in northern Italy), because the conductor Toscanini felt they would interrupt the pace of the opera and drew attention to individual singers as opposed to the work. Toscanini had, in 1887, been challenged to a duel after stubbornly refusing an aria's encore. Wagner was similarly against encores. The ban at the Metropolitan was explicit in the printed programs at the beginning of the 20th century, but was nevertheless often broken at the insistence of the audience. Encores at the Met became rarer later in the century. Popular music In most circumstances, it has become standard for rock, metal, and pop artists to