After the fall of Troy, Aeneas led an army of surviving Trojans to Italy. King Latinus favored the Trojans and agreed to a marriage between Aeneas and his daughter Lavinia. However, the subjects of Latinus did not agree with their king, and other Italians were also hostile to the Trojans. It became obvious that the Trojans would have to fight a coalition of Italian armies, led by Turnus, an unsuccessful Rutulian suitor for the hand of Lavinia.
Aeneas needed help, so he and some of his follows visited Evander, the leader of a Greek colony that had settled on the Palatine. After forging an alliance with Evander, Aeneas went still farther from his camp to obtain further help from the Etruscans.
The goddess Juno, who hated the Trojans, thought that Turnus could obtain an easy victory if he attacked the Trojans while Aeneas was absent. So she sent Iris, the goddess of the rainbow, to tell Turnus about the golden opportunity that he presently enjoyed.
Turnus heeded the message. Soon a sizable army was approaching the Trojan camp. Messapus, an ally of Turnus, was in charge of the foremost line of battle. The sons of Tyrrhus, the herdsman of Latinus, led the troops in the rear. Between these two forces were valiant soldiers commanded by Turnus himself.
In accordance with instructions that Aeneas had given them, the Trojans did not leave the camp to fight Turnus in the open. Instead, they manned the walls and prevented Turnus and his men from entering their camp.
Frustrated by the tactics of the Trojans, Turnus realized that the Trojans could not defend their ships if they remained in their camp. He decided to burn them.
The wood of these ships had come from a pine forest sacred to Cybele, the mother of the gods. For this reason, Cybele did not want these ships to suffer any harm. Therefore, with the permission of Zeus, she changed the ships into marine deities before Turnus could burn them. Turnus and his Rutulian followers watched in horror while the ships broke their chains, dived into the water, and emerged as lovely maidens.
To soothe the troubled hearts of his followers, Turnus pretended that this was a favorable omen. He claimed that this miracle proved that the gods were angry at the Trojans, since they were thereby deprived of their ships. In reality, the miracle had taken place because the Trojans had arrived at their destination and did not need their ships any more.
After a lengthy speech encouraging his soldiers, Turnus told his men to rest. It was too late in the day to engage in further fighting.
During the night, some enemy soldiers watched the gates of the Trojan camp so that none could escape, while others patrolled the area. Trojan soldiers were also busy. Under the guidance of Mnestheus and Serestus, they inspected and improved their fortifications. Fearing a night attack, there were always some Trojan soldiers keeping watch. Lest the watchmen become drowsy, they were relieved periodically.
The Trojans wanted to inform Aeneas about the enemy attack and urge him to hurry back to camp. While Nisus and Euryalus were serving as watchmen, they observed the enemy soldiers who were supposed to be watching the gates. They were overconfident. They had been drinking wine and consequently fell asleep. They had allowed their fires to smolder. Nisus and Euryalus figured that they could easily sneak past the enemy, so they volunteered to serve as messengers to Aeneas.
When they came to the sleeping enemy soldiers, the two messengers killed many of them. Then they continued their journey.
A cavalry contingent under Volcens happened to spot the two messengers. To escape, Nisus and Euryalus ducked into a forest. Euryalus lost his way. When Nisus noticed that his friend was not with him, he retraced his steps. He saw his friend vainly struggling with the enemy. By hurling javelins, he killed two enemy soldiers, but Volcens killed Euryalus. To avenge the death of his friend, he charged into the enemy ranks. He managed to reach Volcens and kill him, but he himself lost his life.
Although the cavalrymen had succeeded in killing the two messengers, they did not rejoice. They mourned their dead captain, and their grief increased when they learned that many of their comrades had been slain.
When dawn shed its light upon the world, Turnus led his warriors into battle. In anger, they impaled the heads of Nisus and Euryalus on pikes and held them high. When the Trojans recognized them, they were filled with grief. The saddest person was the mother of Euryalus.
A trumpet sounded and the battle began. The enemy moved foreword in close formation. They positioned their shields above themselves in such a way that they formed a roof over the advancing soldiers. This was known as the turtle formation.
There was a trench surrounding the Trojan fort, except on one side, along which the Tiber River flowed. The enemy soldiers tried to fill this trench with earth. They also tried to break down the rampart. Some attempted to scale the wall with ladders.
In response, the Trojans thrust at the enemy with poles and hurled stones and all kinds of weapons on them, but it was difficult to break the shield cover that the enemy enjoyed. They finally dropped a huge mass down on the uplifted shields, so that the turtle formation was undone.
After this, these particular soldiers changed their tactics. Instead of trying to break into the fortification, they shot missiles at the defenders.
Elsewhere, Italian warriors were still trying to fill the trench, break down the ramparts, and scale the walls. Both sides suffered casualties.
The Trojans had an especially formidable tower that the enemy was especially anxious to destroy. Turnus managed to set it on fire. It collapsed, resulting in many Trojan casualties. Only Helenor and Lycus escaped injury, and they were killed by the enemy.
The valiant Turnus proved to be a formidable opponent, but Numanus, his brother-in-law, did not fare well. He was an obnoxious braggart, and hurled shameful insults at the Trojans. Though Ascanius had never before engaged in combat and was too young to fight, the insults angered him; so he killed Numanus with an arrow.
Apollo decided to talk to Ascanius. He assumed the form of an elderly Trojan named Butes. While approving of the young man’s bravery, Apollo told him to withdraw from the battle. He then discarded his human disguise and suddenly vanished.
Various Trojan chiefs saw the god and heard what he said to Ascanius. Therefore, they prevented Ascanius from engaging in further combat.
In the meantime, two Trojan brothers named Bitias and Pandarus were overconfident. They opened the gate that they were supposed to guard and started fighting the enemy face to face. When their efforts met with success, some Trojan warriors left the fortification and ventured to fight outside.
When Turnus heard that one of the gates were open, he eagerly rushed to the spot. His presence turned the tide of battle. Turnus even killed Bitias.
Pandarus quickly shut the gate. Some of the Trojan warriors managed to slip back inside before the gate closed, but others were left outside and had to fight the enemy as best they could. Even worse, Turnus managed to enter before the gate closed.
With a little help from the goddess Juno, Turnus killed Pandarus and many other Trojans. He had the opportunity to open the gate and let in his fellow soldiers. If he had done so, that would have been the end of the war. However, in his ardent zeal to fight, he failed to perform this simple operation.
After Turnus had done considerable damage, Jupiter commanded Juno to stop helping him. Encouraged by Mnestheus and Serestus, the Trojans were then able to compel Turnus to leave. Pressed hard by the united Trojan army, he suffered a few wounds. He slowly retreated to a place on the rampart where he could jump into the Tiber River. The water washed his wounds, and he rejoined his comrades. He was glad to get away.
This summary is based on the Latin text of the Aeneid presented online by the Latin Library. I also consulted an offline English translation by Allen Mandelbaum.