The bad leadership of the retreating army allowed the Roman general to pursue it as if it were beaten, and to destroy a portion of the contingents that had remained to the last. But the consequences of the victory were not confined to this. As Caesar advanced into the western cantons of the Belgae, one after another gave themselves up as lost almost without resistance; the powerful Suessiones (about Soissons), as well as their rivals, the Bellovaci (about Beauvais) and the Ambiani (about Amiens). The towns opened their gates when they saw the strange besieging machines, the towers rolling up to their walls; those who would not submit to the foreign masters sought a refuge beyond the sea in Britain.

But in the eastern cantons the national feeling was more energetically roused. The Viromandui (about Arras), the Atrebates (about St. Quentin), the German Aduatuci (about Namur), but above all the Nervii (in Hainault) with their not inconsiderable body of clients, little inferior in number to the Suessiones and Bellovaci, far superior to them in valour and vigorous patriotic spirit, concluded a second and closer league, and assembled their forces on the upper Sambre. Celtic spies informed them most accurately of the movements of the Roman army; their own local knowledge, and the high tree-barricades which were formed everywhere in these districts to obstruct the bands of mounted robbers who often visited them, allowed the allies to conceal their own operations for the most part from the view of the Romans. 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. The Roman central division forced the Viromandui down the declivity. But the right wing, where the general himself was present, was outflanked by the far more numerous Nervii the more easily, as the central division carried away by its own success had evacuated the ground alongside of it, and even the half-ready camp was occupied by the Nervii; the two legions, each separately rolled together into a dense mass and assailed in front and on both flanks, deprived of most of their officers and their best soldiers, appeared on the point of being broken and cut to pieces. The Roman camp-followers and the allied troops were already fleeing in all directions; of the Celtic cavalry whole divisions, like the contingent of the Treveri, galloped off at full speed, that from the battle-field itself they might announce at home the welcome news of the defeat which had been sustained. Everything was at stake. The general himself seized his shield and fought among the foremost; his example, his call even now inspiring enthusiasm, induced the wavering ranks to rally. They had already in some measure extricated themselves and had at least restored the connection between the two legions of this wing, when help came up - partly down from the crest of the bank, where in the interval the Roman rearguard with the baggage had arrived, partly from the other bank of the river, where Labienus had meanwhile penetrated to the enemy's camp and taken possession of it, and now, perceiving at length the danger that menaced the right wing, despatched the victorious tenth legion to the aid of his general. The Nervii, separated from their confederates and simultaneously assailed on all sides, now showed, when fortune turned, the same heroic courage as when they believed themselves victors; still over the pile of corpses of their fallen comrades they fought to the last man. According to their own statement, of their six hundred senators only three survived this day.

After this annihilating defeat the Nervii, Atrebates, and Viromandui could not but recognize the Roman supremacy. The Aduatuci, who arrived too late to take part in the fight on the Sambre, attempted still to hold their ground in the strongest of their towns (on the mount Falhize near the Maas not far from Huy), but they too soon submitted. A nocturnal attack on the Roman camp in front of the town, which they ventured after the surrender, miscarried; and the perfidy was avenged by the Romans with fearful severity. The clients of the Aduatuci, consisting of the Eburones between the Maas and Rhine and other small adjoining tribes, were declared independent by the Romans, while the Aduatuci taken prisoners were sold under the hammer en masse for the benefit of the Roman treasury. It seemed as if the fate which had befallen the Cimbri still pursued even this last Cimbrian fragment. Caesar contented himself with imposing on the other subdued tribes a general disarmament and furnishing of hostages. The Remi became naturally the leading canton in Belgic, like the Haedui in central Gaul; even in the latter several clans at enmity with the Haedui preferred to rank among the clients of the Remi. Only the remote maritime cantons of the Morini (Artois) and the Menapii (Flanders and Brabant), and the country between the Scheldt and the Rhine inhabited in great part by Germans, remained still for the present exempt from Roman invasion and in possession of their hereditary freedom.

The turn of the Aremorican cantons came. In the autumn of 697 Publius Crassus was sent thither with a Roman corps; he induced the Veneti - who as masters of the ports of the modern Morbihan and of a respectable fleet occupied the first place among all the Celtic cantons in navigation and commerce - and generally the coast-districts between the Loire and Seine, to submit to the Romans and give them hostages. But they soon repented.

When in the following winter (697-698) Roman officers came to these legions to levy requisitions of grain there, they were detained by the Veneti as counter-hostages. The example thus set was quickly followed not only by the Aremorican cantons, but also by the maritime cantons of the Belgae that still remained free; where, as in some cantons of Normandy, the common council refused to join the insurrection, the multitude put them to death and attached itself with redoubled zeal to the national cause.

The whole coast from the mouth of the Loire to that of the Rhine rose against Rome; the most resolute patriots from all the Celtic cantons hastened thither to co-operate in the great work of liberation; they already calculated on the rising of the whole Belgic confederacy, on aid from Britain, on the arrival of Germans from beyond the Rhine. Caesar sent Labienus with all the cavalry to the Rhine, with a view to hold in check the agitation in the Belgic province, and in case of need to prevent the Germans from crossing the river; another of his lieutenants, Quintus Titurius Sabinus, went with three legions to Normandy, where the main body of the insurgents assembled. But the powerful and intelligent Veneti were the true centre of the insurrection; the chief attack by land and sea was directed against them. Caesar's lieutenant, Decimus Brutus, brought up the fleet formed partly of the ships of the subject Celtic cantons, partly of a number of Roman galleys hastily built on the Loire and manned with rowers from the Narbonese province; Caesar himself advanced with the flower of his infantry into the territory of the Veneti.