Circus music is music that accompanies the circus. Traditional circus music tries to create a sense of spectacle, while contemporary circus's job is to convey atmosphere and help the story.
Music in traditional circuses is usually played loud and by a band. One of the most famous (if not THE most famous) circus music played in traditional circuses for 100 years is “Entrance of the Gladiators”. Also known as an “Entry of the Gladiators” and “Thunder and Blazes”, it was composed by Czech composer Julius Fučík in 1897 under the name “Grande Marche Chromatique” (he later changed the title based on his interest in the Roman Empire). Canadian composer Louis-Philippe Laurendeau rearranged the “Entrance” for a small band and started selling it across North America. It became popular as a “screamer march” (march played fast) for circuses and is often used to introduce clowns. Another traditional circus march is "Barnum and Bailey's Favorite" by Karl King. "Sobre las Olas", or "Over the Waves", written by a Mexican composer Juventino Rosas, is a waltz commonly played during trapeze shows. Fred Jewell and Henry Fillmore also composed screamer marches for circuses. There is only one song that is never played during the regular show: John Philip Sousa's “Stars and Stripes Forever”. This song is played in case of emergencies, such as animals getting loose or fire, as a signal to workers that something is wrong.
Music for contemporary circuses is often written exclusively for presented shows, and most contemporary circuses don't use commercial music. Others use punk, rap, dance, and other genres of music. Contemporary circuses use music to help dramatize the show's themes, not just as a way of raising adrenaline.
Circus music has its life outside of the circus too. Musicians like Danny Elfman and Tom Waits use circus music in their works. There is even a whole genre of music called “Dark Cabaret”, which is heavily influenced by circus music and music from burlesque and vaudeville.