When these arrived on the Sambre not far from Bavay, and the legions were occupied in pitching their camp on the crest of the left bank, while the cavalry and light infantry were exploring the opposite heights, the latter were all at once assailed by the whole mass of the enemy's forces and driven down the hill into the river.

In a moment the enemy had crossed this also, and stormed the heights of the left bank with a determination that braved death.

Scarcely was there time left for the entrenching legionaries to exchange the mattock for the sword; the soldiers, many without helmets, had to fight just as they stood, without line of battle, without plan, without proper command; for, owing to the suddenness of the attack and the intersection of the ground by tall hedges, the several divisions had wholly lost their communications.

Instead of a battle there arose a number of unconnected conflicts.

Labienus with the left wing overthrew the Atrebates and pursued them even across the river.