By the mid 1st century BC the Roman military had grown accustom to the new style of fighting brought about through the Marian Reforms. Gone were the days of velites and principes financing their own equipment before marching off to war. Now the state supplied their new legionnaires with their own equipment and men of all social backgrounds dressed in the now universal infantry panoply. Cavalry and skirmishers were now composed of irregular auxilia troops, allies, previously conquered peoples or even hired mercenaries. The military was now most certainly new, but was it really improved as well?
The barbarian Gallic and Germanic tribes had been a thorn in the side of the Roman peoples for centuries. Responsible for multiple raids into Roman territory and even managing to sack the city in 390 BC, the Gauls were no friends of Rome. With the resolution of more pressing conflicts with foes in the far east as well as the sorting out of multiple civil disagreements, the Romans were finally able to focus their attention to conquering and subjugating the violent Gallic tribes. Led by the legendary Julius Caesar himself, the Romans found early success in their conflicts with the barbarians with victories at Bibracte and the Battle of the Axona. Fearing for further Roman incursion into their lands the barbarians began forming alliances and confederations amongst themselves to help halt the seemingly unstoppable spread of Roman conquest. As Caesar finished placing the standard of Rome in western Gaul he began to make his way east, placing him at odds with the Nervii and a group of smaller Gallic tribes known collectively as the Belgae. The two armies finally met in a violent conflict near the River Sabis in modern day northern France.
Caesar and his eight legions arrived at the Sabis sometime in 57 BC and took position on top of a hill overlooking the Sabis river with six of his legions, the other two, recently recruited legions, were tasked with escorting the baggage train and would act as a reserve force if any action did take place. With each individual legion numbering about 5000 men and Caesar in possession of eight legions, a rough estimate places their total number at somewhere around 40,000 fighting men. Across the Sabis was another hill which, unlike the clear Roman hilltop, was covered with thick trees and vegetation where 60,000+ Nervii and thousands more of their Belgic allies were hiding unseen. The visible contingent of the Belgae was made up of a few cavalry and skirmishers.
The initial conflict of the battle was a minor skirmish between the visible Belgic cavalry and Roman auxilia cavalry, slingers and archers. Rome’s actions were met with success as the barbarians were sent running back into the woods. It is speculated the Belgae fled hoping the Romans would pursue into the woods and be ambushed by the true barbarian army, however, the Romans refused to follow them up the hill.
The Belgae’s hope for ambush had not run out, however. When the Roman baggage train that had been lagging behind the already arrived six legions appeared on the horizon, the Belgae charged from their hiding places on the hill and attacked. The Roman Cavalry and skirmishers that had just chased back the Belgic cavalry were quickly overwhelmed. The unexpected charge had sent the main Roman army, who was at the time building and fortifying their position, was sent into chaos as men scrambled around camp trying to get their armor on. Caesar flew around camp trying to get as many men as he could organized which he would need if he had any hope of countering the Belgae’s ambush. Forunately, the Roman legionnaires were able to organize themselves, and having been in battle before, could decide on proper course of actions to take. Also, Caesar had commanded his Legates to stay close to their own legions while in camp allowing the legion to organize under their intended commanders. Without these two advantages, the battle would have been over before it began. Thankfully, the swiftness of the Roman response allowed them to present a sufficient force to combat the Belgae.
The ninth and tenth legion won their battle on the left flank and twice drove the Belgic cavalry across the River. The seventh and twelfth legions on the right flank however, had allowed themselves to be outflanked by the Belgic cavalry, some of whom began attacking and looting the camp. Caesar flew to the right side of the battlefield and began rallying his troops to fight harder. Encouraged by the presence of their general, the Romans held.
The two legions in charge of the baggage train charged into the camp and managed to drive the enemy form the hill. The tenth legion, fresh off their victory on the left flank, proceeded to assisting the struggling right flank. With the Romans now possessing the upper hand the last remaining Nervii fought on, until finally breaking and fleeing the field.
Caesar states that of the original 600 Nervii “senators” only 3 survived the conflict while less than 500 of the original 60,000 Nervii fighters were still alive. With the Nervii nearly eradicated entirely and their Belgae allies severely weakened, Caesars conquest of Gaul was completed. Caesar, author of the account of this battle, does not mention how many casualties the Romans suffered heavily implying that he was ashamed at the loss of Roman life as a result of the Nervii ambush. The dominant factor that contributed to Roman victory wasn’t strategy, weapons or numbers, but rather the experience and veteran leadership of the Roman army not only allowed them to hold off total destruction, but also even come out of the Sabis the victor. A less experienced army would have had no chance to quickly organize and fend off the barbarian attack, however, due to Caesar’s legions previous battle experience, they were familiar enough with the practice of battle to form up and counterattack without direct orders from their general. The losses were probably still heavy, but a Pyrrhic victory is better than a devastating defeat.
[Caesar, Commentarii de Bello Gallico Book 2]