During Catulus' consulship, the Romans found out the wandering Cimbri and Teutones were planning to invade Italy. Catulus, as junior consul, was sent to defend the passes through the Alps from Noricum against the Cimbri while the senior consul, Gaius Marius, campaigned against the Teutones and their allies the Ambrones in Gaul. While he was up in the Alps, Catulus pacified much of the territory's tribes with the help of Lucius Cornelius Sulla, who served Catulus as a legate. Catulus found his task impractical, because there were multiple passes and he would have to divide and weaken his army; he decided to retreat to a more defensible position. During the retreat Catulus became worried the Cimbri would corner his army; therefore he decide to attempt to score a minor victory in order to extricate his troops from the region. He led his army onto a mountain, which overlooked the Cimbri camp, and then ordered his men to remain ready for battle while he had a camp raised in view of the barbarians. When night fell Catulus attacked the Cimbri, then used the chaos this caused to cross a stream and continue his march southwards. Catulus marched until he reached the Atesis River; there he ordered his men to construct fortifications on both sides of the river with a bridge between them. When the Cimbri arrived, they made camp and investigated Catulus' defences. Their scouts reported they could not cross the river anywhere in the immediate area, so they decided to dam the Atesis by throwing earth, rocks, and trees into the stream creating a makeshift dam. Unnerved by the diminishing water flow the Romans started to break camp. Catulus unsuccessfully tried to get his troops back to their stations. When the Cimbri finally launched their assault, they found just one cohort defending the camp on the far side of the river. These men fought with courage and somehow managed to escape. Catulus had retreated in the face of the enemy twice, but he had kept his army intact. The following year (101) his command was prolonged and he was given proconsular powers.