At the back row of the orchestra, usually three in number, sit the trombone section, but why three and how long have they been there? Tom Service reflects on their history and the ways in which they are employed. He looks back on over five hundred years of the story of the trombone and offers insight into the meaning of things such as 'Tower Music' and 'Stadtpfeifer'. Tom looks at the role of the trombone in religious music and in music for the theatre, and at its comparitively late arrival within the symphony orchestra, back in the final decades of the 18th Century. And there's a chance to enjoy some of the distinctive qualities that trombones offer to the orchestral music of Beethoven, Schumann, Brahms, Shostakovich and Berg. This week's guest expert is the principal trombonist of the Halle Orchestra, Katy Jones.