Idomeneo, Mozart's first great opera, was the result of a commission from the Elector Karl Theodor of Bavaria. In 1778, the Elector had moved his court to Munich from Mannheim, where Mozart stayed nearly six months during his journey to Paris. By the time he commenced work on the opera in October 1780, Mozart, not yet 25, already had nine operas to his credit.
The libretto chosen was not new, having already been set by the French composer André Campra nearly 60 years earlier; for Mozart's purposes it was revised by Gianbattista Varesco, a Salzburg chaplain. Set on the island of Crete, it recounts the legend of the return of the Cretan king, Idomeneo, to his homeland at the end of the Trojan War. Beset by a storm, Idomeneo promises Neptune a human sacrifice if he and his crew are saved. That the potential sacrifice turns out to be the king's own son, Idamante, becomes the central conflict of the drama.
Idomeneo is often incorrectly termed an opera seria, a static, outmoded form which by Mozart's time had undergone considerable transformation at the hands of Jommelli and others. Although it retains certain elements of the style (da capo arias, for example) Idomeneo's extensive use of the chorus, flexibility, and strong sense of action betrays a strong sense of the libretto's French origins; this observation is underlined by the inclusion of tableaux of the kind that appear in the operas of Rameau and Gluck. The opera concludes with an extensive ballet, an essential component of all French opera, but then only recently introduced to Italian opera by reformers such as Traetta.
One of the great glories of the work is the orchestration. Mozart obviously relished writing for the large and outstanding orchestra attached to the Elector's court, many of whose members had formerly belonged to the Mannheim orchestra, the finest in Europe. The score he produced includes pairs of flutes, oboes, clarinets, and bassoons along with four horns, two trumpets, three trombones, and strings; it is the richest of all his operatic scores, and it drew contemporary criticism for being "too much filled up with accompaniments."
Dramatically, too, Idomeneo shows a marked advance on the traditional opere serie Mozart had composed in Italy less than a decade before. That he had now become a complete man of the theater is shown in a remarkable correspondence with Varesco, who remained in Salzburg after Mozart had gone to Munich to work with the singers. The letters show Mozart not only tailoring the arias to the needs of his singers, as was customary, but also acutely aware of what would and would not work dramatically.
Idomeneo was given its first performance at the Residenz Theater on January 29, 1781; the spectacular staging was particularly praised in the sole contemporary account that was preserved. The opera was not taken up elsewhere, doubtless in part due the demanding orchestral writing, but also because its mixture of Italian and French styles was confusing to contemporary expectations. Mozart did adapt and revive the opera in Vienna in 1786, but Idomeneo has had to wait until the twentieth century to be fully accepted into the repertory.