Opera seria acquired definitive form early during the 1720s. While Apostolo Zeno and Alessandro Scarlatti had paved the way, the genre only truly came to fruition due to Metastasio and later composers. Metastasio's career began with the serenata Gli orti esperidi ("The Gardens of the Hesperides"). Nicola Porpora, (much later to be Haydn's master), set the work to music, and the success was so great that the famed Roman prima donna, Marianna Bulgarelli, "La Romanina", sought out Metastasio, and took him on as her protégé. Under her wing, Metastasio produced libretto after libretto, and they were rapidly set by the greatest composers in Italy and Austria, establishing the transnational tone of opera seria: Didone abbandonata, Catone in Utica, Ezio, Alessandro nelle Indie, Semiramide riconosciuta, Siroe and Artaserse. After 1730 he was settled in Vienna and turned out more librettos for the imperial theater, until the mid-1740s: Adriano in Siria, Demetrio, , Demofoonte, Olimpiade, La clemenza di Tito, Achille in Sciro, Temistocle, Il re pastore and what he regarded as his finest libretto, . For the librettos, Metastasio and his imitators customarily drew on dramas featuring classical characters from antiquity bestowed with princely values and morality, struggling with conflicts between love, honour and duty, in elegant and ornate language that could be performed equally well as both opera and non-musical drama. On the other hand, Handel, working far outside the mainstream genre, set only a few Metastasio libretti for his London audience, preferring a greater diversity of texts.
