In 54 B.C., during the fall and winter when there normally was no fighting and armies went into winter quarters, there was insufficient food for all the Roman legions in Gaul to be housed together as had been the custom, so Caesar dispersed the troops under the commands of the quaestor and legates. By splitting up the men, the burden of providing grain for the troops could be shared by a variety of Gallic tribes. Where each legion settled they set up camp and were expected to stay put for the duration of the winter unless ordered otherwise.
"One of them he gave to C. Fabius, his lieutenant, to be marched into the territories of the Morini; a second to Q. Cicero, into those of the Nervii; a third to L. Roscius, into those of the Essui; a fourth he ordered to winter with T. Labienus among the Remi in the confines of the Treviri; he stationed three in Belgium; over these he appointed M. Crassus, his questor, and L. Munatius Plancus and C. Trebonius, his lieutenants. One legion which he had raised last on the other side of the Po, and five cohorts, he sent amongst the Eburones, the greatest portion of whom lie between the Meuse and the Rhine, [and] who were under the government of Ambiorix and Cativolcus. He ordered Q. Titurius Sabinus and L. Aurunculeius Cotta, his lieutenants, to take the command of these soldiers."Some Gallic tribes were chafing under the Romans and saw the relatively small numbers at each camp as irresistible targets they, with their far superior numbers, could easily defeat. The first of the revolts was a victory for the Gauls and an example of the treachery the Romans would later suffer at the hands of the Germans at Teutoberg Forest. Although Caesar lost this important battle, he defeated the tribes in the other Gallic revolts of the off-season.
Caesar's Gallic Wars Book V. XXIV
Defeat of Cotta and SabinusIndutiomarus had been one of the rival leaders of the Gallic tribe known as the Treveri (whose capital was in the area that is now Trier, Germany), but Caesar had supported his rival, Cingetorix. Angry with the Romans, Indutiomarus was quick to jump at the opportunity for revenge. When he saw that the Romans were distributed in small groups among the Gallic tribes for their winter downtime, he made plans to attack the legion that was under the Roman legate Labienus' command. First, he enlisted the support of other tribes who were also chafing. The Belgic tribe of Eburones (from northeastern Gaul), under their leaders Ambiorix and Catuvolcus, and supplemented by some of the Nervii (a Belgic tribe from northern Gaul), decided to strike the Romans even before Indutiomarus was ready.
Stationed in Eburonian territory were the 15 cohorts led by legates Cotta and Sabinus. The Romans were easily capable of deflecting the first attack from the Eburones, but then Ambiorix came to tell them of a conspiracy of the Gallic tribes to attack all the wintering legions on the same day. Ambiorix said that Cotta and Sabinus' troops should join one of the other Roman winter camps nearby and offered to get them through.
Although Cotta and Sabinus were under orders to stay where they were, Sabinus persuaded Cotta to go along with the offer. The next morning the Romans headed out. The Eburones were in hiding. As the Romans passed their hiding spots, they came out and slaughtered the Romans. Only a few stragglers survived. These headed to Labienus to report their massacre.
Quintus Cicero's CampNext, the Nervii attacked the small forces stationed in their land under the command of Quintus Cicero. Cicero's men repulsed them. Then the Nervii, with allies from the Atuatuci (a Germanic tribe) and Eburones, besieged the Romans. Cicero tried to get messengers through to Caesar, but had a hard time of it. Eventually, word did reach Caesar, who was stationed behind Belgic lines in Samarobriva (modern Amiens). Caesar lacked enough men to act promptly and decisively, so he sent word to his quaestor, Crassus, to come to him. Crassus was to protect the baggage train and hostages Caesar had been guarding, while Caesar, with his one legion, would rush to Q. Cicero's aid.
After Crassus arrived in Samarobriva, Caesar set out, hoping to be joined by other legions en route. Although Caesar sent a message attached to a spear into the besieged camp, Cicero's men learned of Caesar's presence simultaneously from the pluming smoke from the farms along the path that Caesar, considering it enemy territory, burned. When the besieging army learned of Caesar's advance, they broke off their siege to attack his forces. Cicero alerted Caesar to the fact that a very large force was advancing.
The Nervii and allies stationed themselves behind a stream on a ridge, which put them at an advantage over and above their vastly superior numbers. Caesar could not fight them where they were. His only hope was to draw them in. The cavalry skirmished the first day and on the second, it did so again, but with a difference. Caesar had ordered his men to draw the enemy cavalry in by seeming to lose the skirmish. They did so, and the Gauls on the ridge, taking the bait followed the foot soldiers. As they started to tear down the Roman walls, the Romans toppled them over on them. This caused the Nervii and allies to flee.
The End of IndutiomarusWhen news of the Roman victory reached Labienus' camp and the Gallic allies stationed before it, the allies withdrew. Indutiomarus brought in his own tribesmen to attack, but Labienus refused to meet his challenge. After some days of this stand-off, the Treveri started to head home. Then Labienus sent his cavalry against them under orders to kill Indutiomarus, but not to kill the others. They obliged, and brought the tribal leader's head back to Labienus. The rest of the Treveri dispersed.
Source: Adrian Goldsworthy Caesar - Life of a Colossus
See these resources on Caesar's Gallic War and the Latin AP Exam - Caesar