Roman–Gallic wars

• 1. Introduction

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  Around 390 BC, a Gallic chieftain named Brennus led his warriors, the Senones, on a march that ended inside the city of Rome itself. They had already smashed a Roman army at the Battle of the Allia. They walked through the city gates without another fight. They looted what they could carry and left. It was the kind of defeat that a civilization does not forget.

  What followed was nearly four centuries of conflict between the Roman Republic and a wide array of Celtic peoples the Romans called Galli, or Gauls. The principal peoples named in Greek and Roman sources include the Senones, the Insubres, the Boii, and the Gaesatae. The wars ranged from the plains south of the Alps all the way to the Atlantic coast of western Europe. They unfolded not as a single campaign but as a slow, grinding process of expansion, reaction, and eventual domination. How did a republic still bleeding from a sack of its own capital turn the tables so completely? And what became of the peoples who once marched on Rome?

• 2. The First Invasions

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  Brennus's raid on Rome was not the only Gallic incursion of the fourth century BC. Gaulish armies had been pushing into Etruria and Latium, sometimes as outright raiders, sometimes apparently as mercenaries serving the cities of Magna Graecia. The Senones in particular had settled lands immediately south of the Alps, in a region that came to be called Cisalpine Gaul, meaning Gaul on this side of the Alps.

  After the sack, Roman sources record a counter-narrative: some traditions hold that a Caeretan army eventually defeated the Gauls and recovered the plunder. Others credit the Roman commander Camillus. The very uncertainty of these accounts tells its own story. Rome was still a city trying to make sense of a humiliation.

  By 367 BC, a Gallic expedition was reportedly crushed by Camillus again, though ancient writers themselves doubted the historicity of that episode. What is more firmly attested is the period from 361 to 358 BC, when Gauls allied with Tibur attacked Roman territory. During that conflict, a Roman officer named Titus Manlius Imperiosus fought a Gallic champion in single combat, killed him, and took the man's neck ring, or torque, as a trophy. He earned the surname Torquatus from that act. A generation later, a young Marcus Valerius Corvus won a comparable reputation by killing a giant Gaul in single combat, an encounter the sources say was aided by a raven, from which he took his own surname Corvus.

  By 331 BC, Rome and the Gauls had reached a peace that would hold for nearly thirty years.

• 3. Coalition Wars and Sentinum

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  In 302 BC, fresh Gallic groups crossed the Alps, and previously-settled Gallic tribes let them pass southward. Some of those settled tribes joined the march. Etruscans came along as well. They raided Roman territory, withdrew with their plunder, and then fell to fighting among themselves before any decisive Roman response was needed.

  The more serious test came in 295 BC, during the Third Samnite War. Rome now faced an alliance of Samnites, Gauls, Etruscans, and Umbrians simultaneously. The coalition dealt Rome an early defeat, but at the Battle of Sentinum, fought under the consuls Quintus Fabius Maximus Rullianus and Publius Decius Mus, Rome broke the alliance apart. Decius Mus performed the ritual of devotio during the battle, consecrating himself to the gods and charging into the enemy to die, sacrificing himself for Roman victory. The coalition was shattered.

  Less than a decade later, the Gauls pressed Rome again. In 284 BC, the Boii, with Etruscan allies, marched on Rome after the Romans had already moved north to relieve the besieged city of Arretium. Rome stopped the combined force at the Battle of Lake Vadimo in 283 BC. Around the same time, Roman power drove the Senones entirely out of their Italian territory. Rome occupied it.

• 4. The Gaesatae and Telamon

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  By 225 BC, the Insubres and Boii had watched Rome absorb the Senones' lands and understood what the pattern meant. They hired a group of Alpine Gauls called the Gaesatae to join them and mounted a major offensive. The coalition struck first, defeating the Romans at Faesulae. But the Romans regrouped. At Telamon, the Romans turned the battle and dealt the Gallic alliance a crushing defeat.

  That defeat opened the way for a deliberate Roman policy of conquest south of the Alps. Rome invaded Insubrian territory in 223 BC. The following year, Roman forces took Clastidium, Acerrae, and Mediolanum in 222 BC, driving deep into what had been Gallic heartland. Then came the Second Punic War, running from 218 to 201 BC, in which Gallic tribes generally aligned with Carthage against Rome. When Carthage lost, the Gauls who had backed that side faced the consequences.

  Rome absorbed Bononia in 196 BC, Placentia in 194 BC, and Mutina in 193 BC. The geographer Strabo recorded that many surviving Boii retreated north across the Alps into the region later called Boihaemum. He added, however, that the territory was probably already home to Boii before the Italian subjugation. The name of a people had outlasted their presence in Italy.

• 5. Beyond the Alps

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  Rome's reach extended across the Alps beginning in 125 BC, when Roman armies moved first against the Salluvii and Vocontii, then turned against the Allobroges and Arverni. At the Battle of Vindalium and the Battle of the Isere River, both in 121 BC, the Romans achieved a decisive result. The Allobrogian territory was absorbed and organized as the Roman province of Gallia Transalpina, which later became Gallia Narbonensis.

  The period around 109 BC brought a different kind of trouble. During the Cimbrian War, the Cimbri defeated the consul Marcus Junius Silanus. Two years later, in 107 BC, the Cimbri and Ambrones, together with their allies the Helvetii, destroyed a Roman army near Agendicum in the Battle of Burdigala. The consul Lucius Cassius Longinus was killed in that engagement. These were not Celtic tribes in the same sense as the Gauls, but they moved through Gallic territory and sometimes drew Gallic peoples into conflict with Rome.

• 6. Caesar and the Final Conquest

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  From 58 to 50 BC, Julius Caesar led a series of campaigns through Gaul that he documented himself in careful detail. The campaigns resulted in near-complete Roman control of the territory between the Atlantic coast and the Rhine. Caesar's own account noted that, during these campaigns, he discovered some Gallic peoples were receiving support from Britain. That discovery prompted him to mount the first Roman military expedition to the island.

  After Caesar, the story did not end cleanly. Between 40 and 37 BC, Marcus Vipsanius Agrippa marched against the Aquitani in response to unrest in Gaul and defeated them. Then from 28 to 27 BC, Marcus Valerius Messalla Corvinus suppressed a revolt in Aquitania, a campaign significant enough to earn him a triumph. The wars that had started with Brennus walking through Rome's gates in 390 BC closed not with a single decisive moment but with a series of mopping-up operations conducted by generals whose names had already moved on to other ambitions. Caesar's written account of the Gallic Wars remains the most detailed primary source for this entire arc of conflict, a chronicle written by the man who finished what Camillus had started.