June 58 BC · Central Gaul (Burgundy) Theater

The Helvetii — a confederation of Swiss tribes numbering perhaps 360,000 people, including around 90,000 warriors — had abandoned their homeland and were migrating westward through Roman-allied Aeduan territory toward the Atlantic coast, displacing tribes as they went. Caesar, newly appointed governor of Gaul, refused to allow the migration and blocked it at the Arar (Saône) River, cutting off the Helvetian rear guard. The main battle came at Bibracte, the great Aeduan oppidum atop Mont Beuvray. The Helvetians attacked uphill but were broken by Roman pilum volleys and the legions' disciplined countercharge. A Helvetian reserve nearly turned Caesar's flank before being driven back. The survivors — perhaps a third of those who had set out — were ordered back to their Swiss homeland.

September 58 BC · Alsace (Rhine plain) Theater

Ariovistus of the Suebi had crossed the Rhine a generation earlier with an invitation from Gallic tribes seeking military aid and had never left — his Germans now occupied the fertile Alsace plain, enslaved local tribes, and demanded tribute. When the Aedui appealed to Rome, Caesar marched north with six legions and demanded Ariovistus withdraw. The German king refused, and the two armies maneuvered for weeks — Ariovistus avoiding pitched battle until Roman supply shortages might force a withdrawal. Caesar forced the issue by blocking the German supply lines. In the battle that followed, the Roman right wing broke the German left immediately, but the Roman left was pushed back until Publius Crassus (Caesar's cavalry commander) sent in the third line as a reserve. The Germans broke and fled to the Rhine; Ariovistus escaped across it with a handful of men.

July 57 BC · Belgica (modern Belgium) Theater

The Nervii were the most warlike of the Belgian tribes, despising the wine and luxury goods the other Belgians traded with Rome and famously hostile to any accommodation. Caesar marched north to subdue Belgica but was ambushed at the Sambre River while his legions were still making camp. The Nervii had concealed their warriors in the forest across the river and attacked before the Romans could form their battle line. For a time the situation was catastrophic: the 12th Legion's standard-bearers were surrounded and being cut down, and Caesar — fighting in the ranks himself — later admitted the battle was nearly lost. He personally grabbed a shield, pushed to the front, and steadied the line. Labienus, having captured the Nervian camp on the other side of the field, sent two legions back to Caesar's aid. The Nervii fought to annihilation rather than flee.

Summer 56 BC · Brittany (Armorica), Atlantic Coast Theater

The Veneti of Brittany were the dominant maritime power of the Atlantic coast — their high-sided, oak-built sailing ships could operate in the heavy Atlantic swells that swamped Roman oared galleys, and they controlled the vital tin trade with Britain. When they seized Roman officers sent to requisition grain, Caesar ordered a fleet built on the Loire River and launched a combined land-sea campaign. In the decisive naval engagement in the Gulf of Morbihan, Roman galleys were initially outmatched by the Veneti's towering ships, which the Romans could neither ram nor board. Caesar's admiral Brutus invented a solution on the spot: iron hooks on long poles to cut the Veneti's rigging. When the wind died unexpectedly, the Veneti ships were left helpless and the Romans swarmed aboard them. The Veneti war fleet — more than 200 ships — was destroyed in a single afternoon.

August–September 55 BC · Southern Britain (Kent coast) Theater

Caesar crossed the Channel with two legions partly from curiosity, partly to punish British tribes who had aided the Belgic resistance, and partly for the political prestige of leading the first Roman army to cross Ocean — the mythic boundary at the edge of the world. The landing was contested: British charioteers and warriors lined the beach, and the deep-drafted Roman transports could not reach shore, leaving soldiers to leap into shoulder-deep water in full armor under missile fire. The eagle-bearer of the Tenth Legion reportedly jumped first, shaming the rest to follow. A beachhead was secured but storms destroyed many ships. Caesar made terms and withdrew before winter, returning to Gaul without any territorial gain.

July–September 54 BC · Southern Britain (Thames valley) Theater

Caesar returned to Britain the following summer with five legions and 2,000 cavalry aboard 800 ships — the largest amphibious operation Rome had ever mounted. This time the landing was unopposed and the army marched inland, crossing the Thames and driving deep into the territory of Cassivellaunus, who had been named supreme commander of British resistance. Cassivellaunus avoided pitched battle, using his chariot warriors to harass the column and cut off foragers. Caesar forced the Thames crossing and captured Cassivellaunus's main stronghold. British tribal politics did the rest: the Trinovantes, rivals of Cassivellaunus, submitted to Caesar and revealed where the stronghold was. Cassivellaunus made terms — hostages, tribute — and Caesar withdrew before another autumn storm season threatened his fleet.

November 54 BC · Belgica (modern Belgium, near Tongeren) Theater

Ambiorix of the Eburones had been a client of Caesar's, receiving gifts and favors. In the autumn of 54 BC, with 15 cohorts — roughly 1.5 legions under Sabinus and Cotta — wintering in Eburones territory, Ambiorix approached the Roman camp under a flag of truce. He warned the two commanders that a great Germanic invasion was planned and advised them to march to the nearest Roman camp. It was an elaborate trap. Sabinus believed him; Cotta suspected treachery; they argued for days. Finally Sabinus prevailed and the column marched — directly into a valley ambush that Ambiorix had prepared. The Roman column was attacked from every side in broken, wooded terrain that nullified their disciplined formations. Both commanders died; the few survivors who reached a hilltop position fought through the night and committed suicide at dawn rather than surrender. Fewer than a handful escaped to tell Caesar what had happened.

February–March 52 BC · Central Gaul (Bourges, Bituriges territory) Theater

The great revolt of 52 BC began with a massacre of Roman merchants at Cenabum (Orléans) on the same night across all of Gaul — the signal for a coordinated rising. Vercingetorix, a young Arvernian aristocrat of remarkable political and military talent, had forged a coalition of tribes and adopted a strategy of denying Caesar supply by destroying towns and food stores. Avaricum (Bourges) was the Bituriges' capital and the richest city in Gaul; Vercingetorix wanted it burned but was overruled by the Bituriges who refused to abandon their home. Caesar besieged it through a freezing February, constructing a massive ramp and siege terrace of timber despite constant Gallic sorties and fire attacks. When a storm drove in the sentries one night, Caesar's legions poured over the walls. Caesar reported the city was put to the sword — out of 40,000 inhabitants, fewer than 800 escaped. Vercingetorix's prediction that the city could not be defended had proved correct.

April–May 52 BC · Arverni territory (near Clermont-Ferrand) Theater

Gergovia was the capital of the Arverni and Vercingetorix's personal heartland — a great oppidum perched on a volcanic plateau nearly 750 meters above the plain, its steep slopes defended by a chain of camps. Caesar invested it with his six legions but faced an impossible position: the Gauls held the high ground, were being fed from behind, and Vercingetorix's army camped on the plateau above. The Aedui, Caesar's most important Gallic ally, defected in the middle of the siege. In a rash assault intended as a limited operation to seize some lower defenses, the legionaries — contrary to Caesar's orders — charged directly up the steep main slope toward the oppidum walls. They were met by a hailstorm of missiles and driven back downhill in disorder, losing 46 centurions and 700 men in the retreat. Caesar called it a retrograde movement; his soldiers called it a defeat. He raised the siege and marched north to reunite his forces.

June 52 BC · Senones territory (Paris basin) Theater

While Caesar faced disaster at Gergovia in the south, his senior legate Titus Labienus commanded four legions in the north, where Paris (then the small island town of Lutetia of the Parisii) sat amid the marshes of the Seine. Camulogenus, an old but capable Gallic commander, flooded the surrounding marshes and positioned himself on the far bank of the Seine to prevent a crossing. Labienus feinted a retreat northward overnight, then reversed, crossed the Seine at a different point, and attacked Camulogenus from an unexpected direction. The battle was sharp: Camulogenus died in the fighting, and his army was scattered. Labienus captured Lutetia and then — receiving news of the Aeduan revolt — marched south to rejoin Caesar, burning the town behind him.

September–October 52 BC · Mandubii territory, Burgundy (Alise-Sainte-Reine) Theater

After the cavalry defeat that forced him to withdraw into Alesia's oppidum, Vercingetorix sent messengers to every tribe in Gaul demanding a relief army — he still commanded 80,000 warriors inside the walls. Caesar's response was the most audacious engineering feat of the ancient world: two concentric rings of fortifications totaling 35 kilometers, with the inner ring (circumvallation) trapping Vercingetorix and the outer ring (contravallation) facing outward against the approaching relief army. The works included trenches, palisades, towers every 24 meters, flooding channels, and fields of concealed iron spikes called lilies. A Gallic relief army of perhaps 250,000 arrived and launched coordinated attacks on the outer ring while Vercingetorix attacked the inner ring from inside. For three days the Romans held both rings simultaneously against overwhelming numbers. On the final day, a massive assault nearly overwhelmed the outer ring at a weak point in the hills; Caesar personally led reinforcements wearing his red cloak so his soldiers could recognize him, and the assault was broken. Vercingetorix surrendered the next morning.

Spring 51 BC · Cadurci territory (Lot valley, southern Gaul) Theater

After Alesia the resistance fragmented into regional pockets. Uxellodunum was a near-impregnable oppidum on a high plateau above the Célé river, held by the last organized Gallic resistance force under Drappus and Lucterius. Caesar arrived to find the siege already in progress and determined to make an example that would end all further resistance permanently. Unable to storm the plateau, he engineered a tunnel to cut off the town's water supply from a spring at the base of the cliff — when the spring suddenly ceased to flow, the townspeople believed the gods had abandoned them and surrendered. Caesar then ordered that all who had borne arms have their right hands cut off — deliberately mutilating them in a way that left them alive to serve as permanent warnings throughout Gaul. He later wrote that the severity was intended to demonstrate what happened to those who chose continued resistance.