Caesar’s own narrative ends with the entry of the legions into winter quarters. This seems to imply that he meant to continue his narrative into the following year but the political chaos at Rome and then the civil war intervened and his narrative was never finished. The book covering his last campaign in Gaul is the work of Aulus Hirtius, one of Caesar’s legates, who completed the work at the request of Caesar’s close friend Balbus. Hirtius’s narrative is our best source for the events of this year but does not have the scope or quality of the work of his former commander. This is most clearly visible in his assertion that the Gauls had an overall war plan at the beginning of 51. He claims that the Gallic tribes had decided that a strategy based on confronting the Romans with a single coalition army had failed and that they now adopted an approach in which the Roman army would be faced with too many simultaneous rebellions to respond to all of them. On the face of it this seems highly unlikely. It would demand a level of consultation and planning among the various tribes that seems impossible. It is much more likely that internal political calculations as well as a continuing underestimation of the threat posed by Caesar’s army determined the war-making policy of the individual tribes.
Leaving his quaestor Mark Antony in charge at Bibracte, Caesar on the last day of 52 moved against the Bituriges who had already suffered heavily at Avaricum. He was accompanied by a guard of cavalry and made his way to the Thirteenth Legion under Titus Sextius, which was too small a force to keep the Bituriges under control, and combined it with the Eleventh under Reginus stationed nearby. After leaving two cohorts behind to guard the baggage Caesar advanced with his customary speed and appeared before the Bituriges were aware of his arrival. He sent his cavalry on a wide sweep, capturing many of the Bituriges who, unaware of his coming, were peacefully working in their fields. Those who were warned in time made their escape to neighbouring peoples but Caesar pursued them relentlessly. He cowed the neighbouring tribes, who abandoned their resistance and so deprived the fugitives of any hope of sanctuary. The Bituriges, unable to oppose Caesar, quickly surrendered. As he had in the case of the Arverni and Aedui Caesar treated them leniently. Once the campaign was over Caesar led his men back to their winter quarters after promising a bonus for their service and returned to Bibracte. He had only been there for eighteen days when a delegation from the Bituriges arrived to complain of an attack by the Carnutes. The attack may have been set in motion by Caesar’s own expedition against them: the tribe, which was seriously weakened by his attack, would have been an attractive target for raiding. Caesar responded immediately. A campaign against the Carnutes would make clear the benefits of being a dependent of Rome and at the same time strike at an important centre of resistance in central Gaul. He took the Sixth and Fourteenth Legions, who were stationed near the Saône on logistical duties, and set out to punish the Carnutes.
The Carnutes were already weakened after having suffered severely during the rebellion. The fate of Cenabum and other towns that had fallen to Caesar had persuaded them to abandon a number of their own and seek safety in temporary shelters scattered over the countryside, even though it was winter. Instead of simply letting his soldiers loose to plunder and burn their lands as he had done with the Bituriges, to spare his men constant exposure to the harsh weather Caesar chose Cenabum as his base and sent out cavalry and auxiliary units to ravage the countryside. These raids were extremely effective and the soldiers returned to Cenabum loaded down with booty. The effects of the weather and the plundering expeditions proved too much for the Carnutes who fled to the neighbouring peoples after suffering greatly.
After these campaigns Caesar considered that there was little threat of any large-scale resistance except among the Belgae. The Bellovaci and their neighbours were planning an attack on the Suessiones, a client of the Remi who lived near modern Soissons. It was less the fate of the Suessiones that concerned him than that of their patrons the Remi. They had been consistently loyal to the Romans even during the rebellion of the year before and had been an important source of supplies for the army. In addition to practical considerations it was absolutely essential that he be seen to offer effective protection to those tribes that supported him. Leaving two legions at Cenabum to keep watch on the Carnutes under Trebonius, he assembled a force of four legions to confront the Bellovaci.
Once he arrived in their territory he sent out cavalry to reconnoitre and to collect prisoners to question about the Bellovaci’s plans. They revealed that most of the tribe had fled except for a few scouts who were captured and brought back to camp. From them Caesar learned that the Bellovaci had assembled a coalition of tribes to oppose him including the Ambiani, the Aulerci, the Caletes, the Veliocasses and the Atrebates. The coalition army had chosen to camp in a naturally strong location on high ground covered with trees and surrounded by a marsh. Their heavy baggage had been hidden out of sight deep in the forests. The precise location is unknown but it was probably in the forest of Compiègne near the town of the same name close to the confluence of the Rivers Aisne and Oise. The Belgae had several leaders but the most important were Correus of the Bellovaci who had earlier conducted successful guerrilla operations against the Romans, and Commius who had served Caesar well in Britain and had been made king of the Atrebates by him but who had joined the revolt and had been one of its major commanders. Commius had sought support from nearby German groups and brought back about 500 cavalry. The Bellovaci and their allies had developed a dual strategy depending on the number of troops Caesar brought against them. If he came with a force no larger than three legions (about 15,000 men) they would face him in battle, but if he had a larger army they would stay in their easily defended position and try to cut off his supplies as Vercingetorix had planned to do. The scarcity of grain and forage in winter would probably have made this an easier task than it had been in the summer of the previous year. Although Caesar does not specify the size of the enemy force, given their plans that might have been perhaps 30,000 men.
The strength of the confederates’ position prompted Caesar to devise a plan to draw them out. If they would engage a force of three legions he would try to persuade them that that was the total of his forces. He placed his three most effective legions, the Seventh, Eighth and Ninth, at the head of the column preceding the baggage, while he positioned the Eleventh at the rear to give the enemy the impression that he only had three legions with him. Perhaps he remembered the attack launched by many of these tribes on his column nearly six years before. His marching formation could be easily reformed to repel an attack or deploy for battle. The Belgae at the approach of the legions, which seemed to be ready for battle, drew up in front of their camp but did not move down from higher ground. They did not engage nor did Caesar, who was surprised at the size of the Gallic force. His plan had failed. He pitched camp facing the enemy with a deep, narrow valley in between. His camp was heavily fortified, with a 12 feet (3.6m) rampart surmounted by a parapet and fronted by a double ditch 15 feet (4.5m) wide with perpendicular sides. These were far more impressive fortifications than the normal marching Roman camp in the field. In addition, towers were constructed on the ramparts with gangways running between them so that the troops would be able to throw missiles at the enemy from two different levels. These defences could be held by a comparatively small garrison, a necessity at this time of year since a number of soldiers were needed for foraging.
Both sides were active and there were often skirmishes between Roman auxiliaries and the Belgae. Nonetheless the Gallic strategy of attacking the foragers was effective. The scarcity of supplies meant that Roman foraging parties were widely spread and that left them vulnerable to attack. The only obvious solution for Caesar was a direct attack on the Gallic camp but the Gauls kept to their camp and the natural strength of the site meant that if he did attack the camp directly he might not succeed and suffer heavy losses. Clearly this was a much more difficult campaign than the relatively easy victories over the Bituriges and Carnutes. He summoned three more legions to join him as quickly as possible. In addition, to defend against the raids on his foraging parties he ordered the Remi, Lingones and other Gallic states to supply additional cavalry. The Belgae set up an ambush using one of the oldest of all tactical tricks. They lured the cavalry of the Remi into the trap by placing a few horsemen where the Remi would easily see them and when the Remi attacked these men they fled back to the much larger cavalry force posted in ambush. The Remi were encircled and sustained heavy casualties.
The attacks and the skirmishing continued until the Bellovaci learned of the approach of the additional legions. The siege of Alesia was still fresh in their minds. They began organizing an evacuation of their camp. The heavy baggage and non-combatants were to form the head of their column, to be followed by their troops. The column was originally scheduled to depart during the night but the need to organize the wagons delayed the column’s departure until dawn, when their preparations were now visible to the Romans. To protect the rear of the column they formed up their infantry in front of their camp facing the Romans. Anxious to stop the enemy’s withdrawal Caesar reconnoitred the marsh and discover a ridge that almost stretched across it to the enemy camp. Only a narrow depression separated it from the enemy’s camp. It is not clear why the ridge had not been found earlier. It may be that the enemy had stationed troops there that hid it from the Romans. Caesar had boards laid over the marsh and quickly crossed it and moved up to the plateau at the top of the ridge. There he drew up the legions in battle formation and set up artillery, as the enemy was still in range.
The Gauls, confident in the natural strength of their position, were ready to give battle. Caesar was equally aware of it so instead of attacking he drew up a screen of twenty cohorts (two legions) and began to build a camp. Once this was completed he posted the cohorts and cavalry with their horses at the ready. Caesar’s new camp created a serious problem for the Bellovaci. They had had to halt their withdrawal as they were afraid that if they began withdrawing the Romans would attack them as they did so. They hit upon a plan to disguise their withdrawal. They collected bundles of straw and piles of twigs and placed them in front of their camp facing the Romans. When they were ready to move they set them alight. Their movements were hidden by the fire and smoke. They withdrew as quickly as they could. The fire and smoke also held the Romans back. Their cavalry was uncertain about what was waiting for them on the other side of the blaze, fearing a possible ambush, and the smoke so obscured their vision that they could not move forward. The Gauls were able to withdraw ten miles in safety and pitched another camp in a second naturally strong position. Despite Caesar‘s claim that they retreated in disorder it is clear that they had executed a well thought out and successful plan. Once in place at their new position they renewed their attacks on Roman foraging parties.
Once again Caesar’s intelligence gathering served him well. He learned that one of their leaders, Correus, had assembled a force 6,000 infantry and 1,000 cavalry to set an ambush near an area rich in grain and forage. Caesar hurried to the spot, sending his cavalry ahead with light-armed infantry dispersed among them, and then cautiously following with the legions. The cavalry and light-armed would screen his approach and would be taken by the enemy for a normal foraging party. The place that the Gauls had chosen for an ambush was an isolated valley that extended no more than a mile in any direction and was ringed by a river and forests. The Roman cavalry advanced into it and the Gauls sprung their trap. With the knowledge that the legions were coming up in support the cavalry fought well and for a long time both sides were evenly matched. Then the pendulum began to swing in the Romans’ favour as both sides became aware of the legions’ approach. Their arrival was decisive. The Bellovaci turned and fled, but the woods and river created a death trap. They prevented easy escape and more than half their force was lost during the flight, including Correus. After such a heavy defeat Caesar feared that the Gauls would once again retreat. Knowing that their camp lay only 7 miles (11.6km) away on the other side of the Oise he brought his troops across it and hurried to confront them.
The defeat proved too much for the Bellovaci, who opened negotiations for surrender. They argued that the loss of so many men had been punishment enough for them and they blamed the revolt on Correus, who was now conveniently dead. Caesar recognized the falsity of their second argument but decided that clemency was preferable to continued fighting. The Gauls persuaded the other rebel states to join in the surrender and spare Caesar the trouble of further campaigning. Commius had escaped and remained irreconcilable. Before the rebellion of the previous year he had been agitating among various tribes to restart the revolt. Labienus had discovered this and sent a unit of soldiers to assassinate him. The attempt failed but it ended any possibility of reconciliation. Later in 51, as winter approached, Commius and his men had fought a skirmish with Roman cavalry that was indecisive. But he had not given up hope of inciting his fellow Atrebates to rise in rebellion. Meanwhile, he used his cavalry to launch a number of raids on Roman supply convoys. Antony, the legate stationed in the area, dispatched a cavalry unit in pursuit and finally, after a number of skirmishes, Commius was defeated, although at some cost. Seeing no hope of success he entered into negotiations with the Romans. He handed over hostages and was ordered to remain where he was and follow orders in the future. Commius asked one thing in return: that he might never again have to look on another Roman, and Antony granted him his wish.
Major opposition was now crushed but many of the Gauls were still not reconciled to the new dispensation. To deal with the continuing resistance Caesar dispatched Fabius with twenty-five cohorts to support the two under-strength legions under the command of Rebilus in the land of the Pictones south of the Loire, in what later formed part of the province of Aquitania. The Fifteenth Legion, which had been with Labienus in winter quarters, was sent to Cisalpine Gaul to guard against attacks on the citizen colonies. Caesar feared a repeat of an attack launched in the previous summer against the settlement of Tergeste in Illyria (modern Trieste) and he remembered the attempt in 52 to invade the province.
Caesar now turned his attention to Ambiorix and the Eburones. Ambiorix had been one of his most consistent and unyielding opponents. He had been behind the destruction of Cotta and Sabinus in 54 and had sought to forge an alliance of Belgic tribes, including the Treveri, to oppose the Romans. A number of attempts to capture him had all ended in failure. This would seem to indicate that he could draw on substantial support from his own people. Unable to capture him, Caesar determined on a strategy that would make the price of supporting him too costly. He sent out columns consisting of legionaries and cavalry to ravage the lands of the tribe and to kill or capture as many of the Eburones as possible. Labienus was sent with two legions against the Treveri, who had as usual been unwilling to meet Roman demands and had operated with Ambiorix in 54. Labienus defeated the Treveri and their German allies in a cavalry battle. Despite the devastation inflicted on the Eburones and the defeat of the Treveri Ambiorix was never taken prisoner.
The subjugation of Aquitania in 57 by Crassus had been incomplete and events there were affected by the rebellion in central and the northern Gaul. A large rebel force had gathered in the land of the Pictones and part of it under a leader of the Andes, Dumnacus, was laying siege to the town of Lemonum (Poitiers), held by the pro-Roman Duratius. Learning of the siege, Rebilus set out to bring help. Nearing the town and reluctant to face the enemy with a weak force he camped in a secure location. When Dumnacus learned of his arrival he broke off the siege and turned to attack the Romans. His assault ended in failure and resulted in heavy casualties; he abandoned the attack and turned back to renew his siege of the town.
While these events were taking place another legate, Fabius, had been in action nearby and had received the submission of a number of tribes. Rebilus informed Fabius of the attack on Lemonum and Fabius set out to lift the siege. As he approached, Dumnacus and his army withdrew over the Loire. Fabius, informed by locals about the route of Dumnacus’s retreat, decided to follow the rebels. Reaching a bridge over the Loire they had used he crossed and sent out his cavalry in pursuit. They caught up with the enemy column while it was still in marching formation and inflicted a severe defeat on it, but despite the losses the Andes continued their withdrawal. The next night Fabius sent his cavalry on ahead to slow the progress of the column. They met stiff resistance as the Andes’ cavalry knew that their infantry was coming up in support. The Romans began to also attack the infantry who had formed a battle line. This was not sound tactics as cavalry usually could not successfully break infantry in formation. Its main effect was to fix the enemy column, which was exactly what Fabius had intended. The battle was not going well for the Roman cavalry when the legions came into view. The Gauls had been unaware of their presence and their sudden appearance created a panic among them. Their formation dissolved and many were killed during the pursuit: 12,000 died and their baggage train fell into Roman hands.
Dumnacus survived the defeat and remained at large. There was still the possibility that he could cause further trouble among the tribes that had joined the rebellion but had not been defeated. Fabius moved quickly and the opposition collapsed. Even the Carnutes, who had caused the Roman so much trouble and had never yet surrendered, finally did so. Dumnacus had now become a liability to the Gauls and had to seek safety in flight.