Described as a "festa teatrale" in two acts, Ascanio in Alba was composed to celebrate the wedding of Archduke Ferdinand of Austria and Maria Beatrice Ricciarda d'Este of Modena in Milan in 1771. The fifteen-year-old Mozart received the commission (along with two others) as a result of the success of his opera seria Mitridate, rè di Ponto, first given at the Teatro Regio Ducale in Milan on 26 December, 1770. The libretto was prepared by an eminent Milanese poet, the Abbé Giuseppe Parini during the summer of 1771; by the time it was approved by the Emperor in Vienna, Mozart and his father had already returned to Milan. He started work at the end of August, completing the entire work, which included ballets, within less than a month. It was first given on 17 October, the second day of the wedding festivities.
The new opera was well received, and three further performances were immediately scheduled. The young Archduke himself was so enthusiastic about Ascanio that he wrote to his mother, the Empress Maria Theresa, suggesting that he might offer Mozart permanent employment at the Milanese court. He was famously repulsed: Maria Theresa's dismissive reply discouraged the idea of employing such "useless people".
In keeping with its purpose as a ceremonial work, the plot of Ascanio is an allegorical idealization of a royal marriage that had been arranged for motives of political expediency. Venus, wishing to see her grandson Ascanius married to the nymph Silvia, devises a strategy to put the girl's virtue to the test. She survives unscathed and the pair are happily united.
Ascanio contains many of the characteristics typical of the serenata, the genre it most closely resembles. There are only two acts (as opposed to the three of opera seria) and considerable prominence is given to the chorus, which played little or no part in the full-scale serious operas of this period. Also typical is the pastoral setting and low level of dramatic incident. While hardly of major importance within the canon of Mozart's stage works, Ascanio contains much music of a lyrical warmth and sensitivity that belies its hasty conception.