Upon completion of his term as Consul in 58 BC, Caesar was appointed governor of Transalpine and Cisalpine Gaul, modern Italy north of the Po River, for five years. His experiences over the next decade would be recorded in detail in his “Commentaries”, including seven books detailing the Gallic wars. Caesar brought loyalists with him as Commanders of his Legions (+/- 5,000 men), each of which consisted of ten Cohorts (+/- 500 men) commanded by Centurions. The army was well organized; legionnaires were well trained; and discipline was harsh. While pay for common soldiers was lower than that for farm labor, the promise of land grants and other spoils were sufficient to attract many of the poor to service. Engineering skills of the Roman army were very high; legionnaires were well trained and well equipped with metal helmets, armor, shields, javelins and short swords. Caesar had well developed military tactical skills, always moving quickly and aggressively against his enemies.
Caesar brought his personal characteristics to the Gallic campaigns, including great determination, enormous confidence, physical courage, strong leadership abilities, and skilled oratory. These traits earned Caesar great respect from his legions, allowing him to rally often outnumbered and inexperienced troops when they were discouraged by hardship; lacking in food and provisions; or trapped, out-positioned or outnumbered in battle. Caesar brought sophisticated political and diplomatic skills, meeting and communicating with tribal leaders, both friendly and opposed; developing understanding, and taking advantage of, shifting alliances and rivalries both between and within tribes; co-opting tribal leaders who allied with him; making and keeping commitments to protect allied tribes; negotiating and honoring surrender terms; rewarding and protecting newly surrendered allies while brutally punishing those who refused surrender, especially those who betrayed Rome’s alliance and surrender agreements.
The population of Gaul consisted of three primary ethnicities, including the Belgae (north); the Aquitainians (south) and the Celtic Gauls (central); the Rhine divided Gaul from the Germanic tribes (east). The three primary ethnicities were separated into numerous smaller tribes. A band of Gauls south of the Alps had sacked Rome in 390 BC, settled in the Po Valley, and then been subjugated by Rome, which went on to colonize Transalpine and Cisalpine Gaul by 125 BC, securing land routes to Spain.
In 58 BC, Caesar’s confronted the Helvetti Tribe, which had begun a mass migration of 350,000 people from modern Switzerland, across Transalpine Gaul, headed for the Atlantic coast, threatening disruption of tribal claims in southern Gaul and Roman trade and military routes to Spain. Caesar stopped them at the Rhone River, and the Helvetti changed course to the north, plundering tribal lands of the Aedui and Sequani, who were allied with Rome. After several encounters, Caesar’s legions defeated the Helvetti and their tribe was dispersed, sold into slavery, or killed. Next, Caesar confronted the invading Germanic tribes led by Ariovistus, who had crossed the Rhine and attacked the Sequani; after failed negotiations, Caesar attacked, defeated and destroyed the Germanic force, driving their remnants back across the Rhine. These campaigns were protective of, and supported by, the affected Gallic tribes who were allied with Rome.
In 56 BC, the Veniti, in southern Brittany, took several Roman soldiers hostage, who had been sent to negotiate grain supplies for the army. The Veneti were heavily engaged in profitable trade with Britain, and hearing of Caesar’s planned expedition there, decided to confront the Romans. Caesar seized their towns along the coast; the Veneti army embarked to their substantial sailed navy; Caesar called the Roman oared navy from Spain; and with the help of a windless day, crushed the Veneti ships and defeated them. To reinforce security of his envoys in the future, Caesar had the entire Veneti ruling council of a hundred men beheaded; the remnants of the captured tribe were sold as slaves or dispersed. While separate legions of Caesar’s army were despatched to defeat tribes in Aquitainia and Normandy; Caesar proceeded along the Pas de Calais and defeated several smaller tribes there, and so subjugated Normandy and Brittany to Roman rule.
Over the winter of 57-56 BC, Caesar expanded his army to eight legions, double the size he had inherited, raising pay and supplying it with funds raised from the Alpine provinces, and by looting of Gallic wealth, including gold and silver from tribal religious sites. Over this time, the Belgae tribes of northern Gaul, who had banned import of Roman wine, organized in response to the threat Caesar posed to their control of northern Gaul. Caesar marched his army north and confronted the Belgae, who broke up their large force and dispersed; Caesar followed, confronted and defeated the divided forces separately; then drove further north, confronting and defeating the Nervii, the largest remaining force in northern Gaul. The Attuatuci tribe continued to hold out in a small walled city, and Caesar laid siege; the tribe surrendered and agreed to terms, but then violated them by attacking the Romans, who responded by sacking the town and selling all 53,000 residents into slavery.
In 55 BC, two allied Germanic tribes, the Usepeti and Tencteri, crossed the Rhine and invaded Gallic tribal lands. Caesar marched north to meet them, fulfilling his promise to protect Gallic tribes who had surrendered and allied with Rome. After minor cavalry skirmishes, the Germanic tribal leaders reported to Caesar’s camp for negotiations, and Caesar, based on the harassing attacks on his cavalry, arrested them, then attacked their main camp, massacring the leaderless enemy force along with their families; Caesar’s army suffered no casualties. Surviving Germanic tribal members ran to the Rhine, threw themselves in and drowned; their arrested leaders remained with the Roman army rather than face the Gauls they had plundered. Caesar’s engineers then built a bridge over the Rhine in ten days, complete with fortifications at both ends, and Caesar marched his army across, pillaging the surrounding countryside, and then returned to Gaul, breaking down the bridge. When news of these events came to Rome, the Senate conducted a debate, led by Cato, who suggested surrendering Caesar to the Germanic tribes for the offense of taking their peace envoys captive, a serious breach of norms. However, Caesar’s long string of dramatic military successes overcame sentiment against him, and the proposed investigation never concluded. However, political jealousy – and fear – of Caesar’s capabilities persisted.
Later in 55 BC, Caesar organized a raid on the south coast of Britain, based on suspicions they had supplied rebellious Gallic tribes. Caesar’s initial envoy was taken hostage, and Caesar led a small landing force across the Channel, to be followed by a larger reinforcement. The landing force was met by a larger Briton force, and was trapped and attacked on the beach. Reinforcements arrived late due to weather and transport problems; scattered infantry waded to shore; Caesar signaled his ships to run in close to shore and fire slings, arrows and bolt-shooting artillery to protect landed force. The Roman infantry organized into haphazard battle formation; fought off the Britons; established a defensive beachhead encampment; and the Britons suspended their attack. A second attempt to deliver cavalry across the English Channel failed in a storm, and the Britons then sieged the beach encampment, cutting off Caesar from any food supply, attacking foraging parties with fast chariots. After one minor, direct encounter, Caesar organized the embarkment of his army and returned to Gaul, barely escaping disaster.
Caesar returned to Britain the next year, 54 BC, with a much larger force, reinforced by allied Gallic cavalry, and with newly designed ships constructed over the winter. The army landed successfully, immediately marching on and overwhelming a crude, inland Briton fortification, dispersing the tribal force. A storm that night destroyed much of Caesar’s anchored vessels; repairs salvaged a smaller fleet. The Britons raised a larger force to the north; Caesar marched to meet it, crossed the Thames, and defeated it, while his contingent at the beachhead simultaneously defeated a raid on his anchored ships. Caesar then organized a crowded embarkment of his army, returning again to Gaul. Subjugation of Britain would be deferred to future Roman generals.
In 53 BC, the Eburone tribe, led by Ambiorix, residing in the Ardennes in far northern Gaul, rebelled, attacking and defeating a nearby Roman garrison, then aligned with the Nervii and Trevor tribes, and laid siege to another Roman garrison. Caesar immediately marched to confront the tribes; positioned his much smaller force in a fortified camp; waited for their attack; then countered and dispersed the larger tribal force, and relieved the seiged garrison. As word spread, more tribes across northern Gaul as far as Brittany joined the rebellion, and Caesar, aided by additional legions from Pompey’s army in Spain, responded by defeating the tribes of Brittany, then devastating the northern Gaul countryside, burning farms and villages, and plundering grain supplies and livestock for his army.
The next spring, in 52 BC, Caesar negotiated pacification with the tribes of central Gaul, and concentrated his reinforced army to the northeast against the continuing rebellion there. Caesar again bridged and crossed the Rhine to cut off reinforcements from Germania, then returning to trap the still-rebellious Eburones, who had begun the rebellion, alone in the Ardennes. Ambiorix escaped, and Caesar announced the open raiding and pillage of their homeland by surrounding tribes, aided by Roman legions, then executed the chief tribal aristocrat who had inspired the revolt, a major violation of norms. With reinforced garrisons maintained through northern Gaul, the populace now terrorized, this stage of the rebellion was put down.
But the brutality toward the northern Gallic tribes, the plunder of Gallic resources and religious sites, the insult of the execution of a tribal aristocrat, served to inspire the next stage of revolt. An alliance of wealthier tribes in central and southern Gaul, who had previously aided and benefited from Caesar’s campaigns, now faced Rome’s permanent domination, reduced self-governance, and lost control of trade. In the winter of 53-52 BC, these tribal leaders, hearing of major civil strife in Rome, took advantage of it, and met, plotted and organized under their appointed warrior leader, a young Avernian aristocrat named Vercingetorix, joined by tribes all the way to the Atlantic coast. This time the army was united, well organized and supplied, and disciplined. They struck Orleans, murdering Roman traders who lived there; then struck north across the Loire, striking tribes newly allied with Rome, who turned and joined the revolt. Caesar, separated from his army, crossed the Alps with German cavalry and a small force of new recruits, and marched toward Orleans, drawing garrisoned Roman legions along the way. Orleans was evacuated; Caesar ordered it sacked and burned; residents who did not escape were sold as slaves. Caesar crossed the Loire and headed north, capturing Novidium. Vercingetorix adopted a strategy to avoid direct confrontation with Caesar’s army, and to pillage and burn areas around the Roman legions, while keeping his own forces together and on the run. Caesar laid seige to Bourges, then burned it, massacring almost all of its 40,000 residents, men, women and children, and seized its grain and livestock. Caesar divided his force, sending one contingent north to modern Paris; and led another force south, where it failed its assault on Gergovia. The army reunited at the Loire, laying extensive double siege works and trapping the Gallic army on a hilltop at Alesia, repelled Gallic reinforcements, and ultimately defeated them. Caesar made peace with the surrendering tribal armies; Vercingetorix was carted back to Rome where, after formal celebrations, consistent with Roman tradition, he was ritually strangled.
In 51 BC, Caesar led his armies winning smaller scale but difficult campaigns against still-rebellious tribes in south and southwest Gaul. All of Gaul had finally been conquered, and with the exception of one rebellion in 46 BC, would remain passive.
The Romans had proven once again that with superior forces, superior engineering, and superior tactics; they could smash any organized opposing army. Caesar had shown that by manipulation of shifting tribal alliances; co-option of tribal leaders; and terrorization of their populace; the Roman legions could also defeat broad guerrilla rebellions. After a decade of warfare, Caesar had imposed Rome’s provincial system of conquest, governance and commerce on all of Gaul, which, along with the rest of the empire, would greatly enhance the wealth of Rome’s aristocracy. Caesar had become one of Rome’s greatest generals, and, as a reformer, had become a feared rival for predominance in the highest ranks of Rome’s political order.