His ballets, notably Swan Lake and The Sleeping Beauty, have never been surpassed for their melodic intensity and instrumental brilliance. Composed in close collaboration with the choreographer Marius Petipa, they represent virtually the first use of serious dramatic music for the dance since the operatic ballet of the German composer Christoph Willibald Gluck. Tchaikovsky also extended the range of the symphonic poem, and his works in this genre, including Romeo and Juliet and Hamlet, are notable for their richly melodic evocation of the moods of the literary works on which they are based.