At this point Labienus heard rumors from his native troops that the Aedui had defected, and Caesar had withdrawn from Gergovia and was speeding toward the Province.[53] The Bellovaci to the north were also preparing war (7.59.1–2). Labienus realized that he had to quit the offensive against Lutetia or be caught between the Parisii and Bellovaci and cut off from Agedincum. Tantis subito difficultatibus obiectis ab animi virtute auxilium petendum videbat (With so many difficulties suddenly thrown in his path, he realized that he had to seek aid from the courage of his resolution) (7.59.6).
That night, he sent the boats that he had brought from Meclosedum, each under a Roman knight, to await him four miles downstream. Five cohorts were left in camp; the remaining five of that legion were ordered to proceed toward Agedincum with all the baggage and making as much noise as possible. Skiffs with splashing oars added to the hubbub (7.60). With three legions, Labienus rendezvoused with the boats and quickly crossed the Sequana. Shortly before dawn, the enemy learned what was happening and thought the Romans were in flight and trying to cross the river in three places. They divided their army accordingly (7.61.1–4) The main body met Labienus at dawn and, in the ensuing battle, were surrounded and annihilated. The Gauls in the camp came at the sound of fighting and were cut down by the cavalry (7.62.1–7). Labienus returned to Agedincum, where he probably received word of Caesar. Leaving there with the whole army, he rejoined Caesar on the third day (7.62.10).
At Alesia Labienus took part in the fierce fighting around the camp of Caninus and Antistius. The camp was in danger of giving way when he arrived with six cohorts. His orders were to hold out as long as possible and then, as a last resort, draw his troops from the walls and sally forth onto the plain (BG 7.86.1–2). Meanwhile under Caesar’s personal leadership, the battle was won everywhere except at the camp. Caesar, dispatching cavalry around the outer fortifications to come upon the enemy from behind, was hurrying toward the camp (7.87.2). A message came from Labienus that the rampart and ditch were no longer defensible, and that with an additional eleven cohorts from the neighboring forts, he was going to break out. Caesar sped to join the fight (7.87.3). His crimson cloak signaled the arrival of the imperator with reinforcements. The enemy renewed its efforts, but the cavalry appeared at their rear. Panic set in, and many were cut down in flight