The battle of Perusia, 310/309 BC, was a Roman victory that forced several key Etruscan cities to make peace with Rome (Etruscan War, 311/310-308 BC).
The war began when the Etruscans besieged the Roman border city of Sutrium. Although the Romans won two victories outside the city they were unable to force the Etruscans to lift the siege, and so the consul Q. Fabius Maximus Rullianus adopted a different plan.
The border between Rome and Etruria was formed by the Ciminian forest, then seen as a trackless wilderness, and one that had never been crossed by a Roman army. According to Livy one of Fabius's officers (either his brother M. Fabius, his half brother L. Claudius, or another officer called Caeso), who had been raised in the Etruscan city of Caere, offered to scout out the forest. Accompanied by a single servant he reached the Umbrian city of Camerinum, and arranged a treaty with that city's senate. He then returned to the Roman camp.
Fabius decided to risk crossing the forest. After tricking the Etruscan outposts on the edge of the forest the Romans were able to pass through the wilderness, and after a day's march took up a position on the Ciminian hills, from where they overlooked the Etruscan heartland, an area that had rarely seen a Roman army. Fabius sent out foraging parties, and then won a battle against a force of local peasants.
The Etruscans responded by raising the biggest army yet. Livy's sources preserve two traditions on the location of the clash between this army and the Romans. In one the battle took place at Sutrium, but in the other it took place close to Perusia, to the north of the forest. This tradition is supported by Diodorus Siculus.
Livy records a detailed account of the battle. The Romans had built a camp on a plain outside the forest. The Etruscans advanced out of the forest, and formed up in battle order at a suitable distance from the Roman camp. Fabius was outnumbered, and the morale of his army appears to have suffered (perhaps supporting the idea that the battle took place at Perusia, where the Romans would have felt quite isolated). Instead of accepting the Etruscan challenge, he ordered his men to remain in their camp all day.
Towards the end of the next night he ordered his men to dig away the rampart of their earthwork camp, and use the soil to fill the ditch. Just before dawn he finally ordered his men to attack. They crossed the now levelled rampart, and caught the Etruscans totally unprepared for battle. Very few Etruscans stood and fought, and most of the army fled either to their camp, or into the nearby forest. The camp was taken later in the day, and according to Livy the Etruscans lost 60,000 men killed or taken prisoner (almost certainly a massive exaggeration).
In the aftermath of this battle the Etruscan cities of Perusia, Cortona and Arretium asked for peace, and were granted a thirty year truce. The remaining hostile cities were able to raise a new army, but this too would soon be defeated, at Lake Vadimo.