The siege of Tolosa (106 BC) is the only recorded fighting in that year during the Cimbric War, and saw the Romans recapture an allied city that had revolted against them.
The Romans had suffered a series of setbacks in Gaul in the years before 106 BC. The consul Marcus Junius Silunus had been defeated by the Cimbri somewhere in the area in 109 or 108 BC, but the Cimbri then disappear from the records, and we have no idea where they went. In 107 BC the consul L. Cassius Longinus was defeated by the Tigurini somewhere in the south-west of France. He was killed in the battle and the survivors had to agree to humiliating terms to secure their safety.
Before these successes the city of Tolosa (modern Toulouse) had entered into an alliance with Rome, and according to Cassius Dio there was even a Roman garrison in the city. The citizens rebelled against the Romans, and chained up the garrison.
The consul Q. Servilius Caepio was given the task of recapturing Tolosa. He was one of the consuls for 106 BC, and this siege is normally placed in that year, but Orosius called him a proconsul in his account of the siege, which would place it in the following year, 105 BC.
Cassius Dio gives us a brief account of the siege. The Romans were let into Tolosa at night by their friends in the city, took possession and looted the city. The most famous aspect of the siege was the capture of the 'treasure of Tolosa', a large amount of gold and silver that was found within the city.
There were several theories about the source of the treasure in antiquity. Strabo reports two. The first is that it was some of the treasure taken from Delphi when it was attacked by the Celts under Brennus in 279 BC. The second, which he clearly preferred, was taken from Poseidonius, who reported that the treasure consisted of 15,000 talents of gold and silver bullion, much of it found in sacred lakes. The treasure of Delphi wouldn't have been in the form of bullion, as that was looted by the Phocians during the Third Sacred War (355-346 BC). Finally the Celtic attack on Delphi was actually defeated, so it was unlikely that any treasure would have been taken away. The gold and silver at Tolosa was probably earned legitimately by the Celts at Tolosa, and then dedicated to the gods.
Dio says that some of the treasure came from Delphi, but that the city was wealthy in its own right.
Orosius reports that 100,000 pounds of gold and 110,000 pounds of silver were taken from the Temple of Apollo at Tolosa.
However valuable the treasure was, or where it came from, it didn't reach Rome. Caelius sent it under guard to Massilia, but it never arrived. Orosius says that the men guarding it were secretly slain and that Caepio was said to have stolen the money. Dio has it stolen by the soldiers themselves. In either case it became a long running scandal, leading to an investigation in Rome. Caelius went on to play an even less creditable role in the Roman defeat at Arausio (6 October 105 BC), so his role at Tolosa was rather overshadowed by this later scandal. Pompeius Trogus even suggested that the defeat at Arausio was punishment for the theft of the treasure.