Book IV begins just after Aeneas has finished the tale of his travels. Dido sits beside him, inflamed with love. She looks to her sister, Anna, for guidance, torn between the promise she made never to love another man after her husband's death on the one hand, and on the other hand the passion that she feels for Aeneas. Anna tells Dido that she should embrace such love, exciting her imagination by talking about the incredible kingdom that the two of them could build together: "If you marry Aeneas, what a city/ and what a kingdom, sister, you will see!" (64-65).
Having decided to pursue Aeneas, Dido leads him around Carthage, displaying its many marvels. Dido begins acting "insane" (102): she begs him to tell her the entire story of his journey again, hugs Ascanius to her, and allows all work on the construction of Carthage to fall idle. Juno, seeing her dear Dido in such misery, asks Venus if she will help her wed the pair, but Venus recognizes that Juno's motive is to move Aeneas's destined kingdom from Italy to Libya. She tells Juno that she does not want war, but that she fears that fate will not be so easily tricked. Nevertheless, Venus offers the queen of the gods her blessing to go and entreat Jupiter. Juno replies that she will do so, but in the meantime she will hatch a plan to strand Aeneas and Dido overnight in the same cave, where they will be united in marriage.
The next day, the palace sets out on a hunt, but Dido and Aeneas are caught in a thunderstorm and seek shelter in a cave. They sleep together, which Dido interprets as "marriage" to make herself feel less guilty. Afterward, Rumor (described as a terrifying monster) carries word of the pair across the land, and it finally reaches the ears of King Iarbas, who had allowed Dido to build Carthage on his territory and is now angered that she did not marry him but instead took a foreigner as a partner. Jupiter hears King Iarbas's rage and sends Mercury to Aeneas with a message: he did not save Aeneas from the Greeks for this; his destiny lies elsewhere, and he must not begrudge Ascanius his great future.
Aeneas is stunned by Mercury's words. He tells his men to ready the fleet in silence. Nevertheless, Dido catches word of his plan and "raves throughout the city" (403). She then attacks Aeneas with what is undoubtedly the finest, most impassioned speech accorded to any woman in the Aeneid, cursing him for taking her honor and then leaving her without a word. Aeneas counters her anger by hesitantly stating that while he appreciates her kindness, he had never agreed to enter into a marriage contract. Again, he mentions his duty to Ascanius and tells her, "Stop your quarrel. It is not/ my own free will that leads to Italy" (491-492). Dido is not swayed by his words; she rails against him once again, cursing his journey. With this, Dido faints, and Aeneas (with only a little hesitation) turns back to his fleet.
Later, Dido watches the fleet raising their sails in the harbor, ready to leave, and she calls for Anna. She asks her sister to go to Aeneas and ask him to give her just a little more time, so that she may learn "how to sorrow" (598). Anna does her sister's bidding, but Aeneas cannot be swayed. At this, the miserable Dido resolves to die. She asks Anna to build a pyre in her courtyard and lay Aeneas's weapons upon it. Anna, believing that Dido simply wishes to rid herself of any remnants of Aeneas, does as she is told. That night, however, Dido constructs an elaborate ritual, with many sacrifices, and cries out another extraordinary lament for Aeneas's love.
Meanwhile, as Aeneas is asleep in his ship in the harbor, he is visited by Mercury, who warns him that the city will soon be ablaze and that he must depart immediately. Aeneas awakens in terror and calls out to his men to set sail. Dido sees the fleet moving out to sea and beats against her breast, cursing Aeneas and crying out to the gods. She asks Barce, Sychaeus's nurse, to send Anna to her to bathe her body in river water and offer sacrifies. Barce goes, and Dido is left alone to mount the pyre. Atop the structure, she grasps Aeneas's sword, mourns the day the Trojans ever set foot on her shores, and with these words - "I shall die unavenged, but I shall die" (909) - she plunges the sword through her chest.
The city is thrown into a panic at word of the queen's death. Anna, hearing the commotion, runs through the crowd to find her sister's body. Crying out, she clutches Dido to her chest and holds her sister as she finally dies. Book IV ends when Juno, looking down on the sorry sight, sends Iris to free Dido from her tormented body.
Except for the goddesses, the female characters in the Aeneid are, by and large, fairly unremarkable. While Juno and Venus are given distinctive personalities and a hand in driving the action of the narrative, most of the mortal women are far more ineffectual and shapeless. Creusa, for example, is only a vague presence in Book II, and she appears to exist largely in order to die, thereby deepening Aeneas's character and freeing him from the bonds of a wife while explaining the presence of his son. Dido, in sharp contrast, is as rich a character as any other in the epic.
Although the gods in the Aeneid frequently meddle in the lives of mortals, Dido is perhaps the clearest example of the potentially tragic consequences of such intervention. Dido is their plaything, and the pain that wracks her body at the sight of Aeneas and his troops fleeing the city is a visceral example of the importance of abiding by one's destiny. Indeed, Dido is one of the few characters in the Aeneid to truly rail against the dictates of fate. She knows that Aeneas is destined to leave Carthage and to begin a new empire, but the love that she feels for him is so overwhelming that she struggles against the will of the very gods. This struggle makes her perhaps one of the strongest, most courageous characters in the tale.
Dido's character serves two other distinct purposes. First, Virgil uses the Dido/Aeneas conflict to explain the antagonistic relationship between Rome and Carthage in the real world, which came to a head during the Punic Wars. More interesting, however, is the notion that Virgil employs Dido in order to reveal Aeneas's humanity. The protagonist usually seems too perfect: a flawless, unfailingly moral paragon of virtue and courage. By creating a situation in which Aeneas reveals his weakness in the face of love, tempted to stray from his fate - forcing his fleet to dock in Carthage for an uncomfortably, irresponsibly long period of time - Aeneas is revealed as not just a goddess-born hero, but as an imperfect man. His decision to give up love for the betterment of future generations is truly difficult for him, making his decision arguably more honorable.
An alternative perspective on Aeneas's behavior in Book IV is that he is, as David Denby writes, a "cold fish" and a "cad." Dido displays genuine sexual passion that is not found anywhere else in the poem (except, perhaps, in Turnus's desire to wed Lavinia), but Aeneas appears unemotional, even cruel in his ability to walk away from his former lover, despite her desperate entreaties. Even though Aeneas is the hero, he does not behave particularly heroically in this episode. Virgil could have chosen to write a scene where Aeneas takes tearful leave from his lover, wrenching himself from her side even though he finds it almost unbearable to inflict such pain upon another human being, but instead Virgil has him behave in a callous (and cowardly) manner, fleeing the city under cover of darkness. Yes, he dutifully follows his destiny by leaving Carthage in search of the city where he is to found Rome, but he leaves a trail of undeniable destruction in his wake. Dido may be the true hero of this Book: she does not have the security of the gods' blessing, but she is so passionate about her love for Aeneas that she is willing to sacrifice everything she has, even though she ultimately takes her own life.
Another interesting aspect of Book IV is its frequent reference to Ascanius. Aeneas is distracted from his destiny by the temptation of love, and he is only able to regain his focus when he realizes that he will not only be depriving himself of an empire, but will be denying his son the great future that awaits him on Italian soil. This circumstance recalls the importance placed on family, as has been seen in Aeneas's relationship with Anchises. The multi-generational aspect of the epic reveals the value that Virgil's contemporaries placed on respecting one's ancestors and providing for one's descendants.