At the opening of Book VI, Aeneas docks on the coast of Cumae in search of the Sibyl of Cumae, Deiphobe. Upon locating the sibyl in her grotto, Aeneas is ordered to sacrifice seven steers. He does so and promises Deiphobe that if the fates allow him to build a city in Italy, he will raise a temple to Apollo and Diana. Finally, the sibyl, possessed by Apollo, makes a prophecy: she tells Aeneas that he will reach the kingdom he seeks, but that the Trojans will suffer through a horrible war over a "foreign bride" (131), and he will have to confront a "new Achilles" (125).
When the sibyl has finished speaking, Aeneas asks her whether he may be permitted to go before the shade of his father, Anchises. Deiphobe tells him how to do so: he must pluck a golden branch from a tree, give burial to a friend of his who is "defiling the fleet with death" (209), and sacrifice black cattle as a peace offering. At first, Aeneas is uncertain which Trojan she is referring to, but upon returning to the camp, he discovers the body of Misenus, dashed on the rocks after challenging the gods. Aeneas buries Misenus and goes out in search of the golden bough. He finds it (with the help of Venus) and sacrifices the steers.
Deiphobe, seeing that Aeneas has completed all of his tasks, sends his companions away; only Aeneas himself may accompany her on the journey to the Underworld. As they approach the horrible monsters guarding the entrance, Aeneas is struck with fear, and he is only calmed when the sibyl tells him that the creatures are nothing more than phantoms that can bring him no harm. The pair approaches the River Styx, where Charon, the boatman, ferries souls to the afterlife. Aeneas notices that some wretched souls are turned away, and the Sibyl explains that only souls whose bodies have been buried may cross. One of those wandering souls is Palinurus, who begs Aeneas to help him across. Deiphobe promises Palinurus that she will send a plague to the residents of the area where his body lies unburied, so that they will give him a proper tomb.
Finally, after some difficulty convincing Charon to allow living souls to pass, Deiphobe and Aeneas cross the river. They pass by Cerberus, the three-headed dog that guards the riverbank, and they pass the souls of deceased infants and those who were wrongfully executed. They then arrive in the Fields of Mourning, where those who have died from the pains of love wander in misery. It is there that Aeneas sees Dido, and he weeps to learn what became of her. Dido's shade refuses to hear his entreaties, and she flees into the woods in a rage to reunite with Sychaeus, her dead husband.
Next, Aeneas passes through the land where the souls of war heroes reside. He is momentarily distracted when he sees Priam's son, Deiphobus, who married Helen following Paris's death but was betrayed by her and put to death. At Deiphobe's urging they move on, and they encounter a fortress guarded by the terrible Tisiphone, wearing a bloody mantle. Horrified, Aeneas asks what the sins were of those who live inside Tartarus, and Deiphobe replies that the souls being tortured within have committed the gravest of sins, such as dishonoring the gods, adultery, and incest.
Finally, Aeneas arrives in the Groves of Blessedness, where he finds Anchises. He tries to throw his arms around his father, but grabs only air. Anchises describes the many wonders of Elysium to Aeneas, and he then focuses on the great future in store for Aeneas and his descendants: "my tongue will now reveal/ the fame that is to come from Dardan sons" (999-1000). When Aeneas notices souls hovering over a river, Anchises explains that the river is called Lethe, and that after drinking from it souls are stripped of any memory of their former lives, then returned to earth to begin life again in a new body. Anchises points out several souls who would have been significant to Virgil's audience, including Romulus, the founder of Rome; Ascanius's descendants; Julius Caesar; and Caesar Augustus himself. Tears spring to Anchises's eyes when he points out the handsome Marcellus, Augustus's heir, who died at a young age.
Book VI ends with Anchises leading Aeneas and Deiphobe out of the Underworld. There are two gates of sleep through which to exit: one made of horn, and the other of ivory. Aeneas and the sibyl choose the ivory gate for their return to earth. Aeneas rejoins his companions, and the fleet sets out to sea once again.
Perhaps more than any other episode in the Aeneid, Book VI exemplifies the purpose of Virgil's epic. Ultimately, Virgil hoped to appeal to Roman audiences by creating a tale demonstrating that they were fated to become a glorious empire, and in particular to Caesar Augustus, his patron, lauding his leadership skills and the moral values that he espoused during his reign. Not only is it clear in Book VI that Aeneas's destiny is set - his descendants are already clearly delineated, as Anchises points out - but there are numerous additional references to his "fate." The sibyl informs Aeneas that he must pluck a golden bough in order to advance to the Underworld, but he will only be able to do so if he is "fated" to do so: "if the Fates have summoned you,/ the bough will break off freely, easily;/ but otherwise, no power can overcome it" (203-205). Unsurprisingly, Aeneas breaks off the bough with ease. Upon entering Elysium, he witnesses a virtual parade commemorating Rome's great future: Anchises points out countless heroes and leaders who are the lucky benefactors of Aeneas's blessed journey.
Part of Book VI was clearly intended to appeal specifically to Casesar Augustus; when Aeneas encounters his soul in the Underworld, Anchises describes the leader as "the mane you heard so often promised--/ Augustus Caesar, son of a god, who will/ renew a golden age in Latium" (1048-1050). Furthermore, by painting a tragic, heroic portrait of Augustus's beloved nephew and heir Marcellus, who died at the young age of 16, Virgil gives the boy an immortality that Augustus would certainly have appreciated.
Perhaps one of the most interesting episodes in Book VI occurs when Aeneas comes upon Dido in the Fields of Mourning. This brief encounter, during which Aeneas weeps upon realizing his lover's sad fate and Dido refuses to hear his entreaties, offers closure to a dramatic, painful episode, and it invests Aeneas with a much-needed measure of humanity. Readers who may have been struck by Aeneas's apparent heartlessness at his leave-taking of Dido will be won back by his tears here. Aeneas's redemption is somewhat undermined by the fact that Dido flees from him into the arms of her beloved husband, Sychaeus.
Aeneas's reunion with Dido also reveals behavior of Dido that appears entirely inconsistent with the dynamic, forceful woman we encountered earlier. Dido is reduced to a voiceless shade with angry eyes, bitterly fleeing the sight of her former lover without so much as a word of chastisement for the wrong he has done her. It is an unsatisfying ending for those who seek a brilliant, tragic love story - perhaps one of the most poignant and passionate opportunities in literary history - and one must wonder whether Virgil intended to revisit this moment and revise it before releasing the work to the public. That is a question, indeed, that haunts the Aeneid in its entirety: since the work was unfinished at the time of Virgil's death, we are left wondering which scenes and lines he still found unsatisfactory.
Later in the chapter, Aeneas's humanity is again emphasized by his response to the myriad horrors of the Underworld. Even this hero is struck by fear and panic at the sight of the monsters that guard the entrance: "Aeneas, shaken suddenly/ by terror, grips his sword ... Had not/ his wise companion warned him they were only/ thin lives that glide without a body in/ the hollow semblance of a form, he would/ in vain have torn the shadows with his blade" (383-389). Moments later, Aeneas is pained by the sight of unburied souls swarming the shores of the River Styx, and he is horror-struck at the sight of Tartarus. His reunion with Anchises is particularly poignant, as Aeneas throws his arms around his father's shade in vain not merely once, but (famously) three times, again revealing the deep and meaningful relationship shared between the generations.