Battle of the Allia

The Battle of the Allia (18th July 390 BCE) took place during the Gallic invasion of Italy by Brennus or Brennius, Chieftain of the Senones, and the Roman Republic.

On 18th July 390 BCE, the battle took place at the confluence of the River Allia and river Tiber, 11 miles (18km) north of Rome.

The Gallic Army marched towards Rome then when they saw the Roman Army, they spread out in a line with their right wing on the bank of the Tiber, whilst their camp was established on a hill.
The Roman Army had been unprepared and was caught by surprise whilst still in Rome. They had rushed to meet the Gauls, intercepting them 11 miles (18km) from Rome beside the Tiber.

The Roman Army lined up in front of the Gallic Army, but when they extended their wings, the centre became dangerously thin and vulnerable.
The Romans sent their weaker reserves to wait on a hill on their right flank.
Brennus immediately sent an experienced detachment to dislodge the reserves from their hill, thinking that they were positioning to attack his force from the rear. The Roman reserves were easily routed.
At this point panic seized the rest of the Roman Army. The Left wing gave up and ran to the Tiber, whilst the Gauls pursued them and massacred those on the bank. The surviving Roman soldiers jumped into the river and fled to the Etruscan city of Veii.
The Right Wing of the Army ran back to Rome.
The battle led to a total rout of the Roman Republican Army, the majority of whom fled into the territory of the Veii,
The Gauls were stunned by how easy their victory had been and marched on to Rome, first spending the night by the river Anio.

Rome had no defensive wall, so the following day the Gauls occupied the empty city of Rome.
The population had been forced to flee to the nearby town of Caere, whilst the surviving soldiers had retreated to the fortress on the Capitoline Hill, intending to hold out there.
The Gauls then plundered the city.

The Senate then made the exiled Roman General, Marcus Furious Camillus (446-365 BCE), Dictator. He was able to raise an army of 12,000 men and marched on Rome.
Camillus fought the war in the streets of Rome until the Gauls all fled.

To cope with continued wars and the threat of rebellion by the Plebeians, Camillus was made Dictator five times until 367 BCE, which was one of the Republic’s longest Dictatorships.
Rome’s first defensive wall, the Servian Wall was built soon after the attack.

Plutarch
Diodorus Siculus
Livy History of Rome
Geoffrey of Monmouth in ‘Historia Regum Britanniae’ (History of the Kings of Britain) has a similar story but refers to Brennus as Brennius.

River Tiber, approximately 11 miles north of Rome