The opening scene introduces Venus and Ascanio, the son she had by Aeneas. (In most classical sources, Venus/Aphrodite is the mother of Aeneas.) The goddess vaunts the charms of Alba and invites her son to go and rule there. She urges him not to reveal his identity to Silvia, a nymph to whom he is betrothed, but to introduce himself to her under a false identity to test her virtue. While shepherds summon their promised ruler, Fauno reveals that the smiling face of Aceste, a priest, is a sign that the day will be a day of supreme happiness. Obeying the goddess, Ascanio pretends to be a foreigner attracted by the beauties of the place. Aceste tells the shepherds that their valley will be the site of a fine city and that they will have a sovereign, Ascanio, before the day is out. He also informs Silvia that she will be Ascanio's bride, but she replies that she is in love with a young man she has seen in a dream. The priest reassures her, saying the young man in her dream can be none other than Ascanio. Venus then appears to Ascanio and asks him to test the girl a little longer before revealing his true identity.
Ascanio spots Silvia among the shepherds and tries to talk to her. The girl immediately recognizes the young man from her dreams. Fauno intervenes and suggests to "the foreigner" (Ascanio) that he should go off and announce the building of Alba in foreign parts. Thus convinced that the foreigner is not Ascanio, Silvia is deeply saddened. She finally decides to accept her fate but declares she never will love anyone else than Ascanio.
Aceste consoles Silvia, saying that her tribulations are about to come to an end. Venus is invoked by a magnificent chorus. Silvia and Ascanio add their voices to the chorus and the goddess descends on her chariot surrounded by clouds. Venus unites the two lovers and explains how she had intended her son to discover the virtue of his fiancée. Aceste pronounces an oath of fidelity and loyalty to Venus, who then retires. It only remains for Ascanio to perpetuate the race of Aeneas and guide the city of Alba to prosperity.