Helvetian Fire

Julius Caesar arrived in Gaul in 58 BC with six legions, enormous debts, and a politician's eye for opportunity. He was 41 years old — old by Roman standards for a first serious military command — but his governorship of Gallia Transalpina gave him the legal authority to operate north of the Alps, and events immediately conspired to give him the pretext he needed. The Helvetii, a confederation of Swiss tribes swollen by an ambitious chieftain named Orgetorix who had since been executed, were abandoning their homeland in modern Switzerland en masse — 368,000 people by Caesar's count, with 90,000 warriors — and migrating westward through Roman-allied territory toward the Atlantic coast. Caesar blocked the Rhône crossing, watched the Helvetii find another route, and then followed them north.

The first great battle came near Bibracte, the massive hilltop oppidum of the Aedui in modern Burgundy, when Caesar turned his column around and attacked the Helvetian rear guard. The fighting lasted most of a day. Three Helvetian tribes in reserve nearly turned Caesar's flank until he stripped the fourth line from its position and sent it against them. By nightfall the Helvetii had been broken; they marched three days before Caesar caught them again and compelled their surrender. He sent them back to their Swiss homeland with just enough grain to plant a spring crop — both because he needed a populated buffer against Germanic pressure and because an empty Switzerland would simply invite German colonization.

The pretext had worked. Caesar was now deep in free Gaul, in the territory of the Aedui, with a mandate that came from his own interpretation of Roman treaty obligations. Within weeks he was receiving delegations from tribes all the way to the Rhine, warning him about Ariovistus — the Germanic king of the Suebi who had crossed the Rhine at Gallic invitation a generation earlier and never left. Ariovistus had occupied the fertile Alsace plain, was extracting tribute and slaves from neighboring tribes, and had recently settled 120,000 more Germans west of the Rhine with plans for more. Caesar sent an ultimatum; Ariovistus refused it with contempt. At the Battle of the Vosges in September, Caesar's legions broke the German infantry after a furious fight, and Ariovistus barely escaped across the Rhine alive. In a single campaigning season, Caesar had given himself the role of Gaul's protector — a role he had no intention of relinquishing.