Cassius Longinus's defeat (107 BC) saw a Roman army defeated and humiliated by the Tigurini, a Helvetian tribe that was raiding across southern Gaul.
This battle is normally associated with the Cimbric Wars, but it isn't clear if there is any direct connection. The Cimbri had first appeared to the north-east of the Alps, where they defeated a Roman at the battle of Noreia (113 BC), before disappearing into Gaul. They reappeared in 109 or 108 BC, probably threatening the Roman province in southern Gaul, and defeated another Roman army, under the consul Silanus. After that they disappear again, not reappearing until 105 BC. However they probably stayed somewhere in southern Gaul, so may have encouraged the Tigurini to also attempt a raid into the same area.
None of our sources give a clear location for this battle. It is sometimes called the battle of Burdigala (modern Bordeaux), presumably because Orosius has the campaign reaching the Atlantic coast. It is also sometimes called the battle of Tolosa, perhaps because Orosius's account of the battle is followed by an accounting of fighting there in the following year. Livy places it in the country of the Nitiobriges, a Gallic tribe based on the borders of Aquitaine, around the Garonne
Orosius gives the longest account of the campaign. The Tigurini, one of the four tribes of the Helveti, must have been raiding across Gaul. The consul L. Cassius Longinus pursued them to the ocean (the Atlantic), but presumably without actually defeated them. He then began to return back to the Roman province of Gaul, when he was ambushed by the Tigurini. Cassius was killed, as was Lucius Piso, a former consul and one of his legates. The survivors fled to their nearest camp, but then had to come to terms with the enemy. A number of hostages, including the surviving tribune, C. Publius, and half of all of their property, were handed over to the Tigurini in return for the safety of the survivors. After his return to Rome Publius was prosecuted by C. Caelius, one of the tribunes of the plebs, for having given hostages, and was forced to flee into exile.
The Periochae of Livy places the battle in the country of the Nitiobriges. The Consul Lucius Cassius Longinus was massaced along with his army by the Tigurini, a tribe that had migrated from Helvetia. The survivors had to give up hostages and half of their possessions and were then released unharmed.
The battle is briefly mentioned in a fragment of Appian's Gallic History, who described the Tigurini as having 'captured a Roman army commanded by Piso and Cassius and sent them under the yoke, as is related in the writings of Paulus Claudius'.
The battle clearly had a long term impact in Rome. Caesar mentions it several times in his account of his own Gallic Wars, in particular when negotationg with Divico, the leader of a delegation from the Tigurini, who Caesar says was the same man who had commanded their army during the battle with Cassius. There was also a family connection - Lucius Piso was the grandfather of Caesar's father-in-law, another Lucius Piso, the father of Caesar's third wife Calpurnia. This was the third defeat of a Roman army at the hands of a northern tribe in a short period of time, following on from the battle of Noreia (113 BC) and Silanus's defeat of 109 or 108 BC, but it was soon to be followed by worse, the destruction of a massive consular army at Arausio in 105 BC.