Caesar's stunning victories in 58 BCE had unsettled the Gallic tribes. Many rightly predicted Caesar would seek to conquer all of Gaul, and some sought alliance with Rome. As the campaigning season of 57 BCE dawned, both sides were busy recruiting new soldiers. Caesar set off with two more legions than the year before, with 32,000 to 40,000 men, along with a contingent of auxiliaries. The exact number of men the Gauls raised is unknown, but Caesar claims he would fight 200,000.

Intervening again in an intra-Gallic conflict, Caesar marched against the Belgae tribal confederation, who inhabited the area roughly bounded by modern-day Belgium. They had recently attacked a tribe allied with Rome and before marching with his army to meet them, Caesar ordered the Remi and other neighboring Gauls to investigate the Belgae's actions. The Belgae and the Romans encountered each other near Bibrax. The Belgae attempted to take the fortified oppidum (main settlement) from the Remi but were unsuccessful and chose instead to raid the nearby countryside. Each side tried to avoid battle, as both were short on supplies (a continuing theme for Caesar, who gambled and left his baggage train behind several times). Caesar ordered fortifications built, which the Belgae understood would give them a disadvantage. Instead of making battle, the Belgic army simply disbanded, as it could be re-assembled easily.