Any insights into the idea behind the roving band?

The band playing on a rotating platform mounted on a moving car was one of the most interesting things about this otherwise not-so-interesting film. Any information on what led the filmmakers to include the band?

And was the band supposed to be something that the characters in the story actually saw? Was it part of their world, or was it just there to help set the atmosphere for the film's audience? In the scene in which Trevoz has stayed so late with the Neuvilles that he has missed the last ferry, I think it was nearly 1:00 am, the band is out playing!