Caesar's arrival in Africa was a comedy of logistics. He had assembled six legions and 2,000 cavalry at Lilybaeum in Sicily, but when he set sail on December 25, 47 BC, wind and poor intelligence about landing sites scattered his fleet across the North African coast. He landed near Hadrumentum with just 3,500 legionaries and 150 cavalry, a fraction of his force. The city garrison refused to surrender. Caesar marched to Ruspina, then to Leptis to collect reinforcements as they trickled in. By early January, he had enough troops to venture out foraging, but supplies remained dangerously thin. On January 4, he set out with thirty cohorts to gather what his army needed to survive.

Titus Labienus was waiting. Once Caesar's most trusted lieutenant during the Gallic Wars, Labienus had defected to the Republican side at the start of the civil war. Now he commanded a force that dwarfed Caesar's foraging party: 8,000 Numidian cavalry, 1,600 Gallic and Germanic horsemen, and substantial infantry. Caesar deployed in a single line to avoid encirclement, archers forward and his meager cavalry on the wings. It was not enough. Labienus's horsemen pushed back Caesar's cavalry and began to envelop the entire formation. In the center, Numidian light infantry peppered the legionaries with projectiles while staying just out of reach of their pila. Caesar ordered his legions to form a circle, the defensive posture of a surrounded army.

In the midst of the fighting, Labienus himself rode to the front line to taunt Caesar's troops, close enough to recognize individual soldiers. A veteran of the Tenth Legion stepped forward, took aim, and hurled his pilum not at Labienus but at his horse, wounding the animal. "That'll teach you, Labienus, that a soldier of the Tenth is attacking you," the veteran growled. The exchange was personal; these men had fought together in Gaul. Now the bonds of shared campaign had dissolved into civil war, and a thrown javelin was all that remained of the old loyalty. Meanwhile, panic was spreading. When an aquilifer, the soldier who carried the legion's sacred eagle standard, tried to flee, Caesar physically grabbed him and turned him toward the enemy.

Caesar's tactical response was characteristically bold. He extended his battle line and ordered every other cohort to face the opposite direction, so that half his force confronted the Numidian cavalry behind them while the other half faced the light infantry to the front. The legionaries charged in both directions simultaneously, hurling their pila and scattering the Optimates formation. The encirclement broke. Caesar began marching back to camp, but Marcus Petreius and Gnaeus Calpurnius Piso appeared with fresh cavalry and infantry to harass the withdrawal. Caesar reformed, drove them off, and finally reached camp with his army battered but intact. He had failed to gather supplies, but he had kept his force alive. In the days that followed, he improvised, converting sailors into light infantry and having his craftsmen manufacture projectiles from scratch, preparing for the campaign that would culminate in his decisive victory at Thapsus.