In 1708, Ottoboni has a magnificent theatre built in his Palace of the Chancellery. Designed by Juvarra and Pellegrini, the theatre comes with one hundred and twenty-seven sceneries. Ottoboni begins the theatrical season of 1710 at his “teatrino ad uso di pupazzi” with Il Costantino pio, which would be followed in the next two years by Teodosio il Giovane and Il Ciro. According to testimonies, the very expensive puppets were “almost four feet high” and made of cardboard or wood; they closely resembled human actors. They were moved on wooden runners and manipulated from below the stage, using a counterbalance system.

Ottoboni employed the best musicians in Rome for his performances: Il Costantino pio is staged with music by Carlo Francesco Pollarolo and set designs by Juvarra. The performance is extremely successful and praised for his sumptuous sceneries, which bring Ancient Rome back to life—Juvarra was skilled in architectural designs. Likely inspired by Thomas Corneille’s Maximian (1662), the play is both spectacular and edifying: these two tones are best expressed in the gorgeous machine representing the allegory of Religion on a cloud, at the beginning of the play; its presence leads to the epiphany of the Holy Cross (I,1). This machine appears another time in the first act, as Costantino (Constantine) is carried on a chariot pulled by slaves during a triumphant procession; or in the grand finale, when the machine makes Faith appear on a luminous throne. The technical virtuosity required to handle pupazzi is suggested in stage indications explaining that Costantino is demounting his horse or that he is wrestling with the conspirators. The character of Planco (Plancus) is the only comic character of the play. He discreetly continues baroque traditions, such as a dressed-up character—here, he is dressed as Licinio (Licinius). In addition to the many changes of scenery, the play features several choral moments, as well as danced interludes to conclude the first two acts (dance of the Cupids; dance of the Shepherds and the Masks).

The play is printed again in 1730 and performed for the king and queen of France as a “festa teatrale”, to celebrate the birth of the Dauphin of France. The libretto mentions another composer—Venetian Battista Pescetti. The allegorical passages and all indications related to machines have disappeared in this version.

The play begins on the banks of the Tiber river, where Costantino (Constantine) is about to fight the usurper Massenzio (Maxentius), son of Massimiano (Maximian), whose crown he stole. The Sky opens, and Religion appears to announce Costantino’s victory to him. Costantino promises to avenge his sister Costanza (Constantia), who was betrayed by Licinio (Licinius): the latter was supposed to marry her and make her queen of Orient, but he joined the enemy. In Rome, Arsace passes on Costantino’s offer of peace to Massimiano, who rejects them. Fausta, Massimiano’s daughter, announces her brother’s defeat: her father asks her to swear fealty to the winner. Arsace, whom the audience believed to be in love with Fausta, gives unclear reasons to explain that he cannot love her. During a triumphant procession, the legitimate Emperor moves with the chariot of Fama (Renown), pulled by winged horses; then Fama promises Costantino victory. When the latter makes a speech to the Romans to bring them peace, Fausta throws herself at his feet. In the procession, Planco, Costanza’s servant, is looking for Licinio. Thanks to a portrait, he recognises Arsace as his mistress’ future husband. Convinced that Licinio betrayed her, Costanza promises that she will take revenge on him.

Informed by Planco, Costanza pretends not to have recognised Licinio—she wants to feel just how badly she was betrayed. Licinio is won by love and reveals himself to her; he manages to make her reconcile with him: she suggests that she remains hidden before she is certain that her brother will be merciful. Drusilla learns from Planco that Costantino no longer has a wife, and that he can therefore become Fausta’s lover. But Massimiliano despairs and asks his daughter to avenge her dead brother by leading Costantino into a trap, at which point Arsace will kill him; then, he promises to marry his daughter with the murderer. Fausta refuses; Costantino finds her as she is crying. When he tells her that he wishes everyone could unite thanks to his peace proposal, she lets him know that his father left to cry from sorrow. He asks her to take him to her father, insistent despite Fausta’s vague warnings. In the forest, Massimiano is waiting for Costantino; he is with Arsace, who vainly tries to talk him into choosing peace. Costantino arrives with Fausta. As he is about to embrace the defeated king, conspirators ambuscade him. Arsace intervenes to save him; so does Fausta. Not knowing who to believe in this confusing situation, Costantino sends the three suspects to prison.

When he tries to find out who the culprits are, Costantino reconciles with Arsace, whom he recognises as Licinio. But Costanza, convinced that her husband betrayed her with Fausta, wants him dead. Announcing that Massimiano is threatening his own daughter as punishment for having saved Costantino, Drusilla tells Costanza the truth. Fausta flees into the forest, looking for her father who went insane. She manages to control him, then denounces herself to Costantino. In the dungeons of the place, Arsace is locked up; Costanza meets him there. Suspecting that the two conspirators, Arsace and Fausta, are meeting, Costantino walks in on them: Costanza, leaving the prison, throws herself at his feet to tell him the truth. In the final scene, Costantino is accompanied by a procession and celebrates peace; he gives up his plan to take revenge. The play ends with two marriages, and Massimiano is said to be on the run. Then, Faith appears, surrounded by the Liberal arts.