Never one to miss an opportunity, Juno sends her messenger, Iris, down from Olympus to inform Turnus that Aeneas is away from his camp. With their leader gone, the Trojans are particularly vulnerable to an attack, so Turnus immediately leads his army toward the enemy camp. The Trojans spot the army coming and secure themselves inside their newly constructed fortress, unwilling to risk an open battle while Aeneas is away. Finding no obvious weakness in their defenses, Turnus decides to circumnavigate the camp and set fire to the defenseless ships anchored on the shore.

The fleet’s destruction seems inevitable, but an old blessing prevents the ships’ incineration. At the fleet’s construction, Cybele—mother of the gods and sister of Saturn—requested her son Jupiter to render the vessels immortal because they were built of wood from trees in her sacred forest. As Turnus and his troops watch the ships burn, the vessels suddenly pull loose of their anchors, submerge , and reappear as sea nymphs. This sign vexes the Latins, but Turnus remains confident and determined to complete his annihilation of the Trojans, portents from the gods notwithstanding. Night falls, and the Latins make camp around the Trojan fortress.

The Trojans know that they must send reports of the Latins’ movements to Aeneas quickly. Nisus and Euryalus, two friends eager for glory and adventure, volunteer to sneak out in the dark of night. The Trojan captains applaud the bravery of the two men. Quietly leaving the fortress, the two find the entire Latin army fast asleep. They pull their swords and begin slaughtering many great captains. When daylight approaches, they finally make their way toward the woods, but not before Euryalus takes the high helmet of a dead Latin captain as a prize. As they approach the forest, a group of enemy horsemen returning to camp through the woods sees the helmet flash in the distance, and rides toward the two Trojans. Nisus manages to escape into the woods, but the horsemen capture Euryalus. Nisus rushes back to save his friend, but in the end both are killed. The Latins put the heads of the two Trojans on stakes and parade them before the Trojan fortress, to the dismay of those inside.

Then the Latins attack. They cross the trenches surrounding the Trojan fortress and try to identify a weak spot in the walls, holding up their shields to block the barrage of spears that the Trojans hurl down from above. There is a high tower standing just outside the main gate, which Turnus lights on fire. Turnus and his men collapse the tower, killing many Trojans inside. The Trojans within the fortress begin to panic, but Ascanius renews their hope, getting his first taste of war when he fires an arrow through the head of Remulus, one of the Latin captains. Their confidence renewed, the Trojans open the gates and surprise the Latins by rushing out in attack, inflicting many Latin casualties in one quick strike. Unfortunately for the Trojans, Turnus joins the fray, suppresses the Trojans’ surge, and begins to force them to retreat to the fortress. The Trojan Pandarus, observing the turning tide of battle, quickly shuts the gates again, allowing as many of his comrades as possible back inside—but letting Turnus through as well. Finally inside the enemy camp, the Latin leader kills Trojans as though it were an easy game. Eventually, though, Turnus is outnumbered, and narrowly escapes by jumping into the Tiber and floating back out to his comrades.

Throughout the poem, interventions on the part of the immortals tend to be spontaneous, responding to mortal affairs as they unfold. But Virgil’s contention, while describing the burning Trojan fleet, that the fleet is immune to fire because of Cybele’s blessing reads as a contrived act of retroactive deus ex machina. Deus ex machina literally means “god from the machine,” and it is a device used to diffuse or solve a seemingly impossible situation by means of the spontaneous act of a divine hand. It is strange that we are not told about the immunity of the ships beforehand, given that we are told, for instance, that when the Trojans eat their own tables they will know they have arrived at their final destination.

Even stranger is the fact that the miraculous transformation of the Trojan ships into sea nymphs, though the result of a god’s work, does not benefit the Trojans at all. Sea nymphs are not fit for sailing, so the Trojans lose their fleet despite divine intervention on their behalf. The Latins ultimately accomplish their mission of rendering the Trojan fleet useless, meaning that the Trojans are unable to flee the battle by sailing back out to sea. They are now grounded, and it is certain that the events of the epic are to be played out on Italian soil. Aesthetically, the transformation of the Trojan ships into sea nymphs is a sublime ending to the journey of a fleet of vessels that, from the epic’s inception, has been buffeted by constant torments and trials. To go down in flames while at anchor ashore would be a fate unworthy of ships that have endured such harshness at sea. Their underwater metamorphosis proves their status as heroic objects of war.

Virgil flirts with the defeat of the Trojans when, after Turnus gains access to the Trojan fortress, the author claims that if it had occurred to Turnus to open the gates and let his awaiting forces into the citadel, the Latins would have won the war then and there. By pointing to the possibility of other outcomes, Virgil heightens the dramatic import of the battle and establishes the Latins as worthy enemies. At the same time, this comment suggests that Turnus is not as amazing as he may seem, as it points out a shortcoming in his cunning and strategy.

In Book IX, Virgil foregrounds the parallels between the Aeneid and the Iliad. Turnus, for example, openly claims to be in the same predicament as the Greek king Menelaus—a Trojan has swept away Turnus’s bride, Lavinia, just as the Trojan Paris made off with Menelaus’s bride, Helen, thus bringing about the Trojan War. Turnus boasts that the Latins will not need to use the trickery of a wooden horse, as Odysseus did to gain entrance to Troy. Rather, he claims, the Latins will defeat the Trojans outright. Knowing the destined outcome of the war, we see that Turnus spells out his doom here: there may be similarities between the Greek-Trojan conflict and the Latin-Trojan conflict, but their outcomes will not be the same. The gods have offered clear signs that the conflict will turn in Aeneas’s favor, but Turnus chooses to ignore them, denying any faith in the oracles of his demise. Turnus is a fearsome warrior who is either too assured of his own ability—a quality that, when combined with defiance of divine powers, is known as hubris—or is resigned to his role as a pure destructive obstacle to the Trojans. He hints at the latter sentiment when he cries, “I have my fate as well, to combat theirs” (IX.190).

The ill-fated journey of the eager young soldiers Nisus and Euryalus provides a poignant counterpoint to the Trojans’ success at staving off the fortress’s siege. Their youthful bravery is extinguished because of Euryalus’s desire for prizes before the completion of their mission. They could easily kill a few Latins and still make it into the forest in good time. Instead, Euryalus concerns himself with the spoils of battle, enabling the Latins to capture him. Nisus’s willingness to sacrifice his own life for his friend is noble but largely useless, as he does not manage to save Euryalus but does manage to stab Euryalus’s killer as he falls to his own death. Following this intense and emotional episode, Virgil offers a brief message of memorial to these two Trojans, writing:

In narrating the episode, Virgil displays his skill at dramatizing the impulsive, emotional nature of friendship and loyalty. With these lines to Nisus and Euryalus, he displays his confidence in his work and legacy, asserting that his poetry can make men immortal.