The Battle of the Allia was fought c. 387 BC[1][2] between the Senones – a Gallic tribe led by Brennus, who had invaded Northern Italy – and the Roman Republic.

The battle was fought at the confluence of the Tiber River and Allia brook, 11 Roman miles (16 km, 10 mi) north of Rome.

Plutarch noted that the battle took place "just after the summer solstice when the moon was near the full [...] a little more than three hundred and sixty years from the founding [of Rome]," or shortly after 393 BC.

According to Livy, they were called to the Etruscan town of Clusium (now Chiusi, Tuscany) by Aruns, an influential young man of the city who wanted to take revenge against Lucumo, whose son had "debauched his wife".

[16] When the ambassadors of the Senones arrived in Rome and demanded the three Fabii brothers be handed over to them, the Senate was pressured by favouritism not to express opinions against the powerful Fabia family.

Livy wrote that "those whose punishment they were asked to decide were elected military tribunes with consular powers [heads of state] for the coming year.

Livy wrote that "in response to the tumult caused by their swift advance, terrified cities rushed to arms and the country folk fled, but the Gauls signified by their shouts wherever they went that their destination was Rome.

In 295 BC, the Romans deployed six legions; four led by the two consuls, and fought a coalition of four peoples (the Samnites, Etruscans, Umbrians and Senone Gauls) in the huge Battle of Sentinum.

Cornell notes that the estimates of the population of Rome in the late 6th century BC, based on the size of its territory range between 25,000 and 50,000, and thinks that the more likely figure is 25,000-40,000.

Such considerations make it unlikely that the size of the population of Roman citizens would have been large enough to provide a military pool of 24,000 or more soldiers at the time of the Battle of the Allia.

Brennus, the Senone chieftain, suspected that to be a ruse and that the reservists would attack him from the rear while he was fighting the Roman army on the plain.

[26] Plutarch wrote that the Gauls encamped near the confluence of the Allia with the Tiber, some 18 km (11 mi) from Rome, and attacked the Romans suddenly.

The Roman left wing was pushed into the river and destroyed while the right-wing withdrew before the Gauls' attack from the plain to the hills and most of them fled to Rome.

Realising that they were defenceless, they decided to send the men of military age, the able-bodied senators and their families to the Capitoline Hill with weapons and provisions to defend the fortress.

They gazed with feelings of real veneration upon the men who were seated in the porticoes of their mansions, not only because of the superhuman magnificence of their apparel and their whole bearing and demeanour but also because of the majestic expression of their countenances, wearing the very aspect of gods.

So they stood, gazing at them as if they were statues, till, as it is asserted, one of the patricians, M. Papirius, roused the passion of a Gaul, who began to stroke his beard – which in those days was universally worn long – by smiting him on the head with his ivory staff.

Despite the anguish at hearing "the shouts of the enemy, the shrieks of the women and boys, the roar of the flames, and the crash of houses falling in", the men were resolved to continue to defend the hill.

One division besieged the hill, and the other went foraging in the territories of the neighbouring cities because all the grain around Rome had been taken to Veii by the Roman soldiers who had fled there.

Some Gauls arrived at Ardea, where Marcus Furius Camillus, a great Roman military commander who had seized Veii a few years earlier, had gone when he was exiled because of accusations of embezzlement.

Livy commented, "Either the Gauls were stupefied at his extraordinary boldness, or else they were restrained by religious feelings, for as a nation they are by no means inattentive to the claims of religion".

Led by Quintus Caedicius, the centurion they chose as their leader, they routed a force of Etruscans who looted the territory of Veii and intended to attack this city.

The Roman soldiers who had fled to Veii ambushed them, put them to flight, seized their camp, regained the booty, and took a large number of weapons.

The Romans reconstituted an army, gathered men who had dispersed in the countryside when they fled Rome and then decided to relieve the siege of the Capitoline Hill.

Diodorus called Manlius Capitolinus Marcus Mallius and wrote that he cut off the hand of the first Senone climber with his sword and pushed him down the hill.

The Gauls now had to say what they wanted because "he [had] come with legal authority to grant pardon to those who asked it, and to inflict punishment on the guilty, unless they showed repentance".

At dawn, Camillus caught up with them and routed them "[of] the fugitives, some were at once pursued and cut down, but most of them scattered abroad, only to be fallen upon and slain by the people of the surrounding villages and cities".

Plutarch mentions an inaccurate story by Heracleides Ponticus and that Aristotle wrote about the capture of Rome by the Gauls and said that the saviour of the city was "a certain Lucius", not Camillus.

Thereafter, the tribunes allowed the election of heads of state and the levy on an army, which drove the rebels from the Tusculum and laid a protracted siege on Levitra.

The wall was rebuilt with a type of yellow tuff, named Grotta Oscura (after its main quarry), which was of much better quality, in the territory of Veii.

[60] The Historia Regum Britanniae, a medieval work of fiction written c. 1136 by Geoffrey of Monmouth on the legendary kings of Britain, depicts Brennus as leading both Britons and Gauls.