- A large army of Boii, Insubres and Gaesatae invades Roman territory and pillages its way to Clusium;
- The Celtic army defeats a praetor near Faesulae or – more likely – Clusium;
- The consuls Lucius Aemilius Papus and Gaius Atilius Regulus win a decisive victory over the Celts at Telamon, but Regulus is killed.
- The consul Papus then invades the territories of the Boii;
- After returning to Rome, he decorates the buildings on the Capitol Hill with captured Celtic standards and torques.
One of the reasons the Romans were eager to make a treaty with Hasdrubal in Spain was that they feared new attacks by the Celts of Northern Italy. These fears were well founded. In 225 BCE, an enormous Celtic army invaded Roman territory. The invasion had been planned by the Boii and Insubres, who had joined forces with semi-professional bands of warriors known as the Gaesatae. Polybius implies that the name means “mercenaries”, but it more likely derives from a Celtic word for “spear” or “javelin” (cf. Latin gaesum). The Gaesatae were fierce warriors who fought almost naked. Their immense courage was their strength, their lack of armour their weakness.
The Celtic invasion of 225 BCE
Polybius claims the Celtic force was made up of 50.000 infantry and 20.000 horsemen and chariots. These numbers are exaggerated, but the Celtic army must have been large all the same. Polybius, citing official records, claims that the Romans and their Italian allies could in theory field up to 700.000 infantry and 70.000 cavalry to counter the threat. Obviously it was impossible to call up so many men all at the same time, and the Romans had to station legions on Sicily and in Southern Italy as well. Furthermore, one of the year’s consuls, Gaius Atilius Regulus, was sent to Sardinia with an army. But the Celts could not make use of all of their forces either. The Veneti and Cenomani had refused to join their coalition and had instead formed an alliance with Rome. As a consequence, the Celts had to use some of their troops to guard their flank.
The Romans did not know on which side of the Apennines the Celtic host would strike. They sent the other consul, Lucius Aemilius Papus, with a large consular army to Ariminum on the Adriatic coast while an unnamed praetor was sent to Etruria with an army which seems to have mostly been made up of Sabines and Etruscans. This praetor performed poorly. The Celts chose to invade Etruria and somehow managed to bypass the praetor’s forces. Pillaging their way southward and gathering huge quantities of loot, cattle and prisoners, they ultimately reached the city of Clusium (modern Chiusi, near the border of Tuscany and Umbria). The Celts were now just a three-day march away from Rome. Suddenly they received news that the praetor’s army was chasing them and turned north again.
If we follow Polybius’ account, the Celts succeeded in bypassing the praetor’s army again and, after a night march, ended up near Faesulae (Fiesole). This is impossible: Faesulae is to the north of modern Florence and at least a hundred kilometres to the north of Clusium as the eagle flies. That is way too far for a night march. It is more likely that the next confrontation took place near Clusium itself. Here the Celts used their cavalry to draw the Romans into battle. The Romans fell for the trap and in the ensuing battle they were badly cut up, losing some 6.000 men. The survivors fled to a defensible hill where they would surely have perished, had not the consul Lucius Aemilius Papus come to their rescue. As soon as he had heard of the Celtic invasion on the other side of the Apennines, he had broken camp and force-marched his troops from Ariminum to Etruria.
The consul arrived just in time. The Celts were laden with booty and decided not to risk losing it in a battle. They subsequently withdrew their forces, following a route to the coast in the direction of Telamon (present-day Talamone). This is another indication that the previous encounter cannot have taken place at Faesulae: Telamon is west of Clusium, but some 140 (!) kilometres south of Faesulae.
The Battle of Telamon
By pure chance, the consul Regulus had left Sardinia and had landed his army near Pisa. He had started marching south, in the direction of Rome. In the vicinity of Telamon, his scouts captured a Celtic foraging party. The foragers provided the consul with all the information that he needed. He now realised that it was possible to trap the Celtic host between Papus’ army and his own, in a genuine baguette of death. Regulus quickly assembled his cavalry and occupied a strategic hill. The Celts, thinking it was actually Papus’ cavalry that had executed a flanking manoeuvre, attacked the hill with their own horsemen and light troops, but they soon realised they were up against the other consul while Papus was still behind them. The Celts now had no other option but to deploy their army into two lines, back to back, with one line facing Regulus’ army and the other that of Papus.
During the opening stages of the Battle of Telamon, the Roman and Celtic cavalry were locked in a fierce struggle over control of the strategic hill. Papus had sent his cavalry up the hill to aid Regulus, who bravely fought in the front ranks. This was risky, and after a while the consul was unhorsed and killed, his head being taken to the Celtic chieftains. But the Roman horsemen fought on and ultimately drove the enemy off the hill. This proved vital for the outcome of the battle. By now, the infantry of the three armies had clashed. The Roman light troops (velites) managed to inflict serious casualties among the Gaesatae who, fighting naked, were particularly vulnerable to missile fire. But the Boii and Insubres, together with a tribe called the Taurisci, fought bravely even though their situation was hopeless. Since they were trapped, they could not retreat and had no choice but to fight to the death. The battle was decided when the Roman cavalry stormed off the hill and hit the enemy in the flank. The Celtic army was all but destroyed.
Polybius claims 40.000 Celts were killed and no less than 10.000 were taken prisoner. These figures are rough estimates and perhaps inflated, but there can be no doubt that Celtic casualties were appalling. Polybius does not give a number for Roman casualties, but these must have been significant as well. Papus, now sole commander of the Roman armies, followed up on his victory by marching north through Liguria and invading the lands of the Boii. After a successful campaign, the consul returned to Rome where he decorated the buildings on the Capitol Hill with captured Celtic standards and torques. This was a highly symbolic action, as during the Sack of Rome by the Celts in 390 (or 386) BCE, the Capitol had been the only part of the city to remain in Roman hands. The consul was also awarded a triumph.
- Cassius Dio, Roman History, Fragments of Book XII (including text by Zonaras);
- Livius, Periochae, Book 20;
- Polybius, The Histories, Book 2.22-2.31;
- Adrian Goldsworthy, The Fall of Carthage, p. 139;
 Florence had not been founded yet. It was founded as a colony in 59 BCE.