Ombra is a term which has been used for an operatic scene involving the appearance of an oracle or demons, witches or ghosts. Such scenes can be traced back to the early days of opera and were commonplace in the seventeenth century in Italy and France. Operas based on the legends of Orpheus, lphigenia and Alcestis provide numerous examples, extending well into the eighteenth century, including works by Jommelli and Gluck. Hermann Abert applied the term to
certain accompanied recitatives by Hasse and Jommelli.
Ombra scenes proved popular with audiences not only because of the special stage effects employed but also because of the increasing use of awe-inspiring musical effects. By the end of the eighteenth century they had come to be associated with an elaborate set of musical features
including slow sustained writing (reminiscent of church music), the use of flat keys (especially in the minor), angular melodic lines, chromaticism and dissonance, dotted rhythms and syncopation, pauses, tremolando effects, sudden dynamic contrasts, unexpected harmonic progressions and
unusual instrumentation, especially involving trombones. Parallels can be drawn between these features and Edmund Burke's 'sublime of terror', thus placing ombra music in an important position in the context of eighteenth-century aesthetic theory.
Music incorporating ombra elements gradually began to appear outside opera, such as in oratorios, in parts of mass settings (especially requiems) and in instrumental music, most frequently in slow introductions to symphonies. Ombra therefore provides a source for topical references for many composers. Mozart especially used the ombra style in his operas (e.g. the Oracle in ldomeneo, the Statue in Don Giovanni) and his instrumental writing (the slow
introduction to the 'Prague' Symphony K504). Haydn's 'Representation of Chaos' in The Creation incorporates several ombra characteristics, as do the introductions to symphonies by Krommer and J.M. Kraus, among others.