The Battle of Arausio took place on October 6, 105 BC, at a site between the town of Arausio (modern day Orange, Vaucluse) and the Rhône River. Ranged against the migratory tribes of the Cimbri under Boiorix and the Teutoni were two Roman armies, commanded by the proconsul Quintus Servilius Caepio and consul Gnaeus Mallius Maximus. However, bitter differences between the commanders prevented the Roman armies from cooperating, with devastating results. The terrible defeat gave Gaius Marius the opportunity to come to the fore and radically reform the organisation and recruitment of Roman legions. Roman losses are quoted at up to 80,000 troops, as well as another 40,000 auxiliary troops (allies) and servants and camp followers. By comparison, the much more famous Battle of Cannae in 216 BC saw around 45,000 Romans killed according to modern scholars, though the ancient Roman historians Livy, Plutarch, and Appian say 50,000, Quintilian says 60,000 and Polybius claims as many as 70,000.
Having regained Tolosa, the proconsul Quintus Servilius Caepio adopted a defensive strategy, waiting to see if the Cimbri would move toward Roman territories again. In October of 105 BC, they did.
The initial contact between the two forces occurred when a detached picketing group under the legate Marcus Aurelius Scaurus met an advance party of the Cimbri. The Roman force was completely overwhelmed and the legate was captured and brought before Boiorix. Scaurus was not humbled by his capture and advised Boiorix to turn back before his people were destroyed by the Roman forces. The king of the Cimbri was indignant at this impudence and had Scaurus executed by being burned alive in a wicker cage.
Meanwhile, Maximus had managed to convince Caepio to move his force to the same side of the river, but Caepio still insisted on a different camp, and actually pitched his closer to the enemy. The sight of two Roman armies gave Boiorix pause for thought, and he entertained negotiations with Maximus.
Caepio, presumably motivated into action by the thought that Maximus might be successful in negotiations and claim all the credit for a successful outcome, launched a unilateral attack on the Cimbri camp on October 6. However, Caepio's force was annihilated due to the hasty nature of the assault and the tenacity of Cimbri defence. The Cimbri were also able to ransack Caepio's own camp, which had been left practically undefended.
With a great boost in confidence from an easy victory, the Cimbri then proceeded to destroy the force commanded by Maximus. Already at a low ebb due to the infighting of the commanders, this Roman force had also witnessed the complete destruction of their colleagues. In other circumstances the army might have fled, but the poor positioning of the camp left them with their backs to the river. Many tried to escape in that direction, but legionaries of the time were not known for their prowess at swimming, and certainly not when encumbered. Certainly, the number of Romans who managed to escape were very few. This includes the servants and camp followers, who usually numbered at least half as many again as the actual troops. Though the actual casualty figure remains debated, Livy claims that the total number of Roman casualties (not including camp followers or other non-combatants) amounted to 80,000. Mommsen claims that besides the 80,000 Roman soldiers, half as many of the auxiliaries and camp-followers perished.
As it turned out, the Cimbri next clashed with the Averni tribe, and after a hard struggle set out for the Pyrenees instead of immediately marching into Italy. This gave the Romans time to re-organise, and elect the man who would become known as the saviour of Rome, Gaius Marius.
Roman chronicles did mention that the soil of the fields the battle had been fought upon were made so fertile by human remains that they were able to produce "magna copia" (a great quantity) of yield for many years.