Turnus gathers his own men and sends a messenger to the city of King Diomedes, a Greek now living in Italy, to try to win him as an ally. Meanwhile, the spirit of the Tiber river appears to Aeneas in a dream, and tells him not to fear the war—he's finally reached his homeland and the destination of his household gods. The Tiber god tells Aeneas to travel up the river until he sees a white sow with piglets (the same that Helenus predicted in Book 3), which will be the sign of the place where Ascanius should build his city, Alba Longa. The Tiber god also says that near this spot live the Arcadian people, in a city called Pallanteum, and that Aeneas should go win the Arcadian king, Evander, to his side. The Tiber god also tells Aeneas to pray to Juno, to make her a little less angry.
It's a good sign for the Trojans that the land itself, in the form of the Tiber, has accepted Aeneas, further indicating his fate to rule this new homeland, despite the coming war. The Tiber's suggestion to pray to Juno seems like a great tactic Aeneas hasn't yet tried, considering Juno's pride and self-importance.
Aeneas thanks the Tiber god and sails with some of his men along the river. They see the white sow, and Aeneas sacrifices it as an offering to Juno. The men continue, reaching the place where someday Rome's towers will rise, a spot now occupied by Evander's humble home.
For the first time in the poem, Aeneas shows piety also towards Juno. His sacrifice of the fated white pig shows his understanding that Juno is involved in his fate.
The Arcardians are in the middle of a feast to honor Hercules and the gods. When they see the ships arriving, Pallas, Evander's son, goes to greet them so that the feast won't be interrupted. Aeneas explains he wants to ally with Evander in the coming war. Pallas is immediately impressed by Aeneas's nobility. Aeneas meets Evander and explains himself. Evander remembers meeting Priam and Anchises as a youth, and quickly agrees to help the Trojans and invites them to join the feast. Evander tells the story of Hercules and Cacus, which the feast commemorates. Cacus, a monster, stole eight of Hercules's cows and brought them to his cave. Hercules heard the cows mooing, and though Cacus blocked off the cave and breathed fire and smoke at him, Hercules managed to strangle him.
Evander's piety towards the tradition of honoring Hercules, as well as his knowledge of Priam and Anchises, makes him a perfect ally for Aeneas. As we saw at Dido's temple, the Trojans are famous throughout the Mediterranean. Here's another place where the same concerns touch the human heart. The story of Hercules and Cacus can also be seen as foreshadowing the war. Will Aeneas manage to pull off a Hercules-like feat, defeating those who stand against and taking what is rightfully his?
Evander gives Aeneas a tour of his city, and tells its history. During the peaceful, plentiful Golden Age, Saturn named this place Latium. But the Golden Age faded, and the land changed rulers many times, until Evander's fate brought him here. They look at the Capitoline Hill, future location of many important Roman temples. They also pass by the future Forum, now a field for grazing.
It would have been fun for Roman readers to picture their city in its countryside form eleven hundred years before. The tour of the pre-Rome area allows Virgil to extol Rome's greatness, suggesting a second Golden Age—the age of Augustus Caeasar.
Venus asks her husband Vulcan to build a set of armor for Aeneas, and kisses him as encouragement. Vulcan says he would even have built armor for Aeneas at Troy, if she'd asked. Vulcan gets his Cyclops workers to build a seven-layered shield.
Just like Juno, Venus is always trying to intervene in events. She's just trying to help, rather than harm, Aeneas. But if Aeneas is fated to win, why would he need her help?
In the morning, Evander and Aeneas meet to talk war. Evander says he would like to fight but is too old, but he advises Aeneas to go ally with the thousands of Tuscans who revolted against Mezentius's tyrannical rule. Those Tuscans already wanted to join the war against Mezentius, but a prophecy had told them to wait for a foreign commander. Evander also offers to send his troops and his beloved young son, Pallas, to fight for Aeneas and learn the ways of war.
Evander's trust in Aeneas, and his willingness to hand over his precious son, shows the depth of the bonds that war establishes between nations. War creates new families and eternal enemies.
Red light, accompanied by thunder, appears in the clear sky. Aeneas explains that it's a sign from Venus that war nears. Evander passionately prays that Pallas will return safely, hoping to die if his son is killed. Aeneas and the soldiers set out, with Pallas leading and looking particularly brave and handsome. The mothers of Pallanteum watch them go and cry.
Evander's love of his son parallels Aeneas's piety to his family. The loving and concerned mothers of Pallanteum who wish that war could be avoided but do not interfere in fated events contrast with the mothers of Lavinium, whom Allecto stirred into a crazy frenzy to start a war with the sole goal of thwarting fate.
Aeneas's group finds the Tuscans and camps with them. As they camp, Venus comes down from the heavens to give Aeneas his new armor. Aeneas marvels at the beautiful helmet, sword, and spear, and finally the ornate shield. On the shield, Vulcan has depicted the future of Rome, including important Roman myths and history such as Romulus and Remus suckling from a she-wolf and Augustus Caesar leading the Roman fleet to victory at the Battle of Actium, along with the celebrations in Rome afterward. Aeneas doesn't know what the images mean, but he appreciates them, and "lift[s] onto his shoulders now the fame and fates of all his children's children."
Other than the trip to the Underworld, this moment represents the place in the Aeneid where Virgil gives the most specifics about Rome's future. He touches on many stories central to Roman culture and even mentions politicians and orators of his time period. The shield gives physical form to Aeneas's fate to create the people who will found Rome, and simultaneously suggests both that all of Rome's future will help guard him in battle, and that Rome's future depends entirely on this one man.