The career of Emperor Justin I is historical fact. Justin, a peasant’s son, was a soldier in Byzantium, rose to the rank of commander of the palace guard and, following the death of the emperor, made use of a court intrigue to have himself crowned. The Venetian lawyer Nicolò Berengani, an accomplished writer, created a libretto for an opera from the story.
During the 1724 carnival season, Vivaldi was again in Rome, where he premiered first a pasticcio and then Il Giustino at the Teatro Capranica. By papal decree, only men were allowed on stage in Rome at that time. Vivaldi did not allow himself to be hampered by this new challenge. Il Giustino requires ten actors and, besides strings and continuo two recorders, two oboes, two trumpets, two horns and two timpani and even, for one aria, a dulcimer.
A report of Vivaldi’s success in the 1724 season comes from the German flautist Johann Joachim Quantz: “The newest thing that I have heard was the so-called Lombardi style that was hitherto entirely unknown to me and that Vivaldi introduced a short time before in his operas in Rome and which enchanted the citizens to such a degree that they scarcely wish to hear anything that is not similar to this style.“