The Cimbrian War (113-101 BC) was fought between the Roman Republic and the Proto-Germanic tribes of the Cimbri and the Teutons (Teutones), who migrated from northern Europe into Roman controlled territory, and clashed with Rome and her allies. The Cimbrian War was the first time since the Second Punic War that Italia and Rome itself had been seriously threatened.
The timing of the war had a great effect on the internal politics of Rome, and the organization of its military. The war contributed greatly to the political career of Gaius Marius whose consulships and political conflicts challenged many of the Roman republic's political institutions and customs of the time. The Cimbrian threat, along with the Jugurthine War, inspired the Marian reforms of the Roman legions, which would have a significant effect on the history of the later Republic.
Rome eventually won the protracted and bloody war — which inflicted the heaviest losses to Rome's armies that they had suffered since the Second Punic War — with the victories at Aquae Sextiae and Vercellae resulting in the almost complete annihilation of the two Proto-Germanic tribes.
Italy was now open to invasion, yet for some reason, the Cimbri and their allies headed west over the Alps and into Gaul. In 109 BC, they invaded the Roman province of Gallia Narbonensis and defeated the Roman army there under Marcus Junius Silanus. That same year, they defeated another Roman army at Burdigala (modern day Bordeaux) and killed its commander the Consul Gaius Cassius Longinus Ravalla. In 107 BC, the Romans lost again, this time to the Tigurines, who were allies of the Cimbri they had met on their way through the Alps.
The consuls led their armies on their own armed migration to the Rhône River near Orange, Vaucluse where they made separate camps on opposite sides of the river. The two Roman commanders disliked and distrusted one another, consequently their armies, instead of acting as a single, overwhelming force, would be separate entities for the Cimbri, Teutones and their allies to destroy in detail. The overconfident Caepio foolishly attacked without support from Mallius Maximus, and his legions were wiped out and his undefended camp overrun. The now isolated and demoralized troops of Maximus were then easily defeated. Thousands more were slain trying desperately to rally and defend his poorly positioned camp. Only Caepio, Maximus and a few hundred Romans escaped over the carnage-choked river with their lives. The Battle of Arausio was the costliest defeat Rome had suffered since Cannae. In fact the losses were far greater and so were the long term consequences. For the Cimbri and Teutones it was a great triumph, yet in it and in their failure to follow up on it were to be sown the seeds of their destruction. Instead of immediately gathering their allies and marching on Rome, the Cimbri went on to Hispania, while the Teutones remained in Gaul. Why they did not, for a second and fatal time, invade Italy remains a mystery. Perhaps they thought easier plunder could be found in Gaul and Spain. Possibly too, they might have suffered heavy casualties in their triumphs over the Romans and felt they were not yet strong enough to take them on their home grounds. With their reckless battle tactics, even their victories could have been rendered costly. Theodor Mommsen describes their methods of war thusly:
Their system of warfare was substantially that of the Celts of this period, who no longer fought, as the Italian Celts had formerly done, bareheaded and with merely sword and dagger, but with copper helmets often richly adorned and with a peculiar missile weapon, the -materis-; the large sword was retained and the long narrow shield, along with which they probably wore also a coat of mail. They were not destitute of cavalry; but the Romans were superior to them in that arm. Their order of battle was as formerly a rude phalanx professedly drawn up with just as many ranks in depth as in breadth, the first rank of which in dangerous combats not unfrequently tied together their metallic girdles with cords. 1So with all these tactical disadvantages, they had to rely on superior numbers, their own fearsome courage and mistakes by Roman commanders to bring them victories. Yet they would soon be faced with a Roman General who seldom made mistakes at the head of a new Roman army which would prove a much deadlier foe.
Up until this time the army had been a well trained, well regulated Militia of all able-bodied, land-owning male citizens. Marius replaced this with a standing, professional force made up mostly of able bodied but landless volunteers. He would improve and standardize training, weapons, armor and equipment. He would improve the command structure and make the Cohorts the main tactical and administrative units of the legions. Along with these new arrangements would come new standards and symbols- the Aquila which he taught his troops to revere and never allow to fall into enemy hands.
While the panicked Senate and people of Rome gave Marius the power he needed to undertake his military reforms, the failure of the Cimbri and Teutones to follow up on their victory would give him the time he needed to finish them. They would soon be confronted by an army of organized, highly trained, professional soldiers under the leadership of a brilliant and ruthless commander.
In 101 BC, the Cimbri returned to Gaul and prepared for the final act of their drama with Rome. For the first time they penetrated through the Alpine passes, which Marius' co-consul for that year, Quintus Lutatius Catulus, had failed to fortify, into northern Italy. Catulus withdrew behind the Po River, leaving the countryside open to the invaders. But the Cimbri took their time ravishing this fertile region, which gave Marius time to arrive with reinforcements — his victorious legions from Aquae Sextiae. It would be at Vercellae near the confluence of the Sesia River with the Po on the Raudine Plain, where the superiority of the new Roman legions and their cavalry would be clearly demonstrated. In the devastating defeat the Cimbri were virtually annihilated, and both their main leaders, Boiorix and Lugius, fell. The women killed both themselves and their children in order to avoid slavery. Thus the war which began with migration, ended in genocide and mass suicide.
It would be over a century later before Rome would suffer another great defeat at the hands of Germanic tribes, at the Teutoburg Forest. And it would be several centuries more before Germanic migrations would again seriously breach the Roman frontiers and threaten the Eternal City itself.
The political consequences resulting from the war, however, would have a much more immediate and lasting impact on Rome. The end of the Cimbrian war would mark the beginning of the rivalry between Marius and Sulla, which would eventually lead to the first of Rome's great civil wars. Moreover, following the final victory at Vercellae, and without first asking permission from the Senate, Marius granted Roman citizenship to his Italian allied soldiers, claiming that in the din of battle he could not distinguish the voice of Roman from ally from the voice of the law. Henceforth all Italian legions would be Roman legions and henceforth the allied cities of the Italian peninsula would seek a greater say in the external policy of the Republic, leading eventually to the Social War.
Marius may have saved Rome from the Proto-Germanic tribes, but he had also initiated the beginning of the end of its Republican form of government. The new soldier class he created of landless, often impoverished legionaries, though they swore an oath to the SPQR, really owed their loyalty to the generals who raised, led and, most importantly, paid them. Generals such as Marius himself, Sulla, Crassus, Pompey, Caesar, Mark Antony, and of course Octavian, would lead the way from Republic to Autocracy.