Borodin's comparably small compositional output appears incredible once one considers that music was not his primary profession. A researcher and professor of chemistry, Borodin also found time to devote to a side-career as a composer. Understandably, then, his larger works took a great deal of time to complete. "Prince Igor," his only opera, took nearly twenty years, and was never finished. Along the way, it accumulated music from Borodin's abandoned projects. Famous for its set of "Polovtsian Dances," "Prince Igor" is set in the medieval era, during which the growing Russian empire battles the Polovsty, a nomadic Central Asian tribe. After Borodin's death in 1887, the opera was completed and edited by his friends and fellow-composers Rimsky-Korsakov and Glazunov.