Julius Caesar is embroiled in a bitter struggle with Pompey the Great for control of the Roman world. In their most recent battle, at Pharsalus (48 BC), Caesar defeated his rival, who subsequently fled to Egypt, which is under the joint rule of Ptolemy and his sister, Cleopatra. Caesar has pursued Pompey to Alexandria.
ACT I. The Egyptian people welcome Caesar to Alexandria (“Viva, viva”). Cornelia and Sextus, Pompey’s wife and son, request that peace be made between the two Romans, and Caesar agrees. Just then, Achillas, the Commander of the Egyptian army, enters with a gift for Caesar from Ptolemy, the King of Egypt: the head of Pompey. Apalled, Caesar tells Achillas that he must go to Ptolemy’s court and meet with the King (“Empio, dirò tu sei”). Sextus assures his mother that he will avenge his father’s death (“Svegliatevi nel core”).
In her apartments in the royal palace, Cleopatra declares the throne will one day be hers alone. Nirenus, her confidante, tells her that her brother has sent Pompey’s head to Caesar. She decides to address Caesar on different and more effective terms (“Non disperar”). Ptolemy enters and the siblings quarrel over who is more fit to be the Egyptian sovereign. After Cleopatra leaves, Achillas tells Ptolemy that his gift to Caesar was not welcomed. He advises his king to have Caesar murdered. Achillas himself will see to the murder if Ptolemy will reward him with Cornelia’s hand in marriage. Ptolemy agrees, although he, too, desires Cornelia (“L’empio, sleale”).
At his encampment, Caesar contemplates the urn containing Pompey’s ashes (“Alma del gran Pompeo”). He ponders the fleeting nature of life. Cleopatra enters and announces herself as “Lydia,” an attendant of Queen Cleopatra. Caesar is struck by her beauty. She tells Caesar that, though she is of noble birth, Ptolemy has deprived her of her fortune. She asks for justice. Caesar tells her that he is going to Ptolemy’s court and will present her request there (“Non è si vago e bello”). Once he has gone, Nirenus assures Cleopatra that she has snared the affections of the Roman. Cornelia approaches to pay her respects to Pompey’s ashes (“Nel tuo seno”). She picks up a sword from the pile of trophies and swears vengeance for her husband’s killing. Sextus assures her that he will fulfill his duty (“Cara speme”). Cleopatra comes forward, still as “Lydia,” and tells them she will help in their quest for revenge. She can help them gain access to the palace (“Tu la mia stella sei”).
In the royal palace, Caesar voices his disapproval of Pompey’s murder to Ptolemy. Left alone, he reflects that the crafty hunter moves silently and unseen (“Va tacito e nascosto”). He departs. Achillas presents Cornelia and Sextus to Ptolemy. The Romans berate the king for Pompey’s murder. As punishment for their bold words, the king orders Sextus confined to the palace and Cornelia to the harem garden. Achillas makes advances to Cornelia but is rejected (“Tu sei il cor”). He leaves mother and son to bemoan their cruel fate (“Son nata a lagrimar”).
ACT II. In the palace garden, Nirenus assures Cleopatra (still disguised as “Lydia”) that Caesar will be fascinated by her. “Lydia” provides entertainment for Caesar, presenting herself as Virtue (“V’adoro, pupille”). Caesar is enchanted (“Se in fiorito”). While Cornelia grieves (“Deh, piangete”), Achillas enters and again courts her. Ptolemy arrives. Achillas tells him that he has been unsuccessful with Cornelia but assures him he will kill Caesar that very day. Cornelia threatens to kill herself (“Cessa omai di sospirare”), but Sextus appears with Nirenus in time to prevent her. Sextus renews his promise to kill Ptolemy (“L’angue offeso”).
Cleopatra calls on Venus to help her conquer Caesar’s affections (“Venere bella”). She pretends to sleep. Caesar enters and is struck by “Lydia’s” beauty. Curius, the Roman Tribune, runs in with the news that the Egyptians are calling for Caesar’s death. “Lydia” reveals her true identity as Cleopatra, Queen of Egypt, and offers her aid in quelling the uprising. She advises Caesar to flee the region, but he intends to master the situation (“Al lampo dell’armi”). Cleopatra, alone and recognizing Caesar’s extreme vulnerability, begs the gods for help (“Se pietà”).
ACT III. Ptolemy emerges victorious from a struggle between his and Cleopatra’s forces; she is now her brother’s prisoner. He puts her in chains and leaves, telling her she will soon kneel before him (“Domerò la tua fierezza”). Cleopatra mourns her fate and is led off (“Piangerò”).
Caesar appears alone by the sea, having survived a drowning attempt in the Alexandria harbor and been left for dead (“Aure, deh per pietà”). He hides as Sextus and Nirenus enter, looking for Ptolemy. They discover Achillas, mortally wounded at the water’s edge. He confesses to the murder of Pompey, asks them to speak kindly of him to Cornelia, and gives them a ring, telling them that a hundred armed men are ready to obey its bearer. He dies. Caesar comes forward and takes the ring from Sextus. He explains his escape from the harbor and orders them to follow as he goes to collect the soldiers and rescue Cornelia and Cleopatra from Ptolemy (“Quel torrente”).
In her apartments, Cleopatra is bidding her attendants farewell when Caesar and the soldiers rush in and free her. He leaves to continue the battle as she rejoices at her sudden turn of fortune (“Da tempeste”).
Ptolemy tries to court Cornelia in the palace harem, but Sextus discovers them and kills the king. Cornelia blesses her avenging son.
Caesar assures Sextus of his friendship and proclaims his love for Cleopatra. He places her on the throne (“Caro, più amabile beltà”) as the people celebrate (“Ritorni omai”).