Nothing remained for the Roman general but, in spite of his inferior strength, to imitate the movement of the Germans, and to recover his communications by making two legions march past the enemy and take up a position beyond the camp of the Germans, while four legions remained behind in the former camp. Ariovistus, when he saw the Romans divided, attempted an assault on their lesser camp; but the Romans repulsed it. Under the impression made by this success, the whole Roman army was brought forward to the attack; and the Germans also placed themselves in battle array, in a long line, each tribe for itself, the cars of the army with the baggage and women being placed behind them to render flight more difficult. The right wing of the Romans, led by Caesar himself, threw itself rapidly on the enemy, and drove them before it; the right wing of the Germans was in like manner successful. The balance still stood equal; but the tactics of the reserve, which had decided so many other conflicts with barbarians, decided the conflict with the Germans also in favour of the Romans; their third line, which Publius Crassus seasonably sent to render help, restored the battle on the left wing and thereby decided the victory. The pursuit was continued to the Rhine; only a few, including the king, succeeded in escaping to the other bank (696).

Thus brilliantly the Roman rule announced its advent to the mighty stream, which the Italian soldiers here saw for the first time; by a single fortunate battle the line of the Rhine was won. The fate of the German settlements on the left bank of the Rhine lay in the hands of Caesar; the victor could destroy them, but he did not do so. The neighbouring Celtic cantons - the Sequani, Leuci, Mediomatrici - were neither capable of self-defence nor trustworthy; the transplanted Germans promised to become not merely brave guardians of the frontier but also better subjects of Rome, for their nationality severed them from the Celts, and their own interest in the preservation of their newly-won settlements severed them from their countrymen across the Rhine, so that in their isolated position they could not avoid adhering to the central power. Caesar here, as everywhere, preferred conquered foes to doubtful friends; he left the Germans settled by Ariovistus along the left bank of the Rhine - the Triboci about Strassburg, the Nemetes about Spires, the Vangiones about Worms - in possession of their new abodes, and entrusted them with the guarding of the Rhine-frontier against their countrymen[37].

The Suebi, who threatened the territory of the Treveri on the middle Rhine, on receiving news of the defeat of Ariovistus, again retreated into the interior of Germany; on which occasion they sustained considerable loss by the way at the hands of the adjoining tribes.

The consequences of this one campaign were immense; they were felt for many centuries after. The Rhine had become the boundary of the Roman empire against the Germans. In Gaul, which was no longer able to govern itself, the Romans had hitherto ruled on the south coast, while lately the Germans had attempted to establish themselves farther up. The recent events had decided that Gaul was to succumb not merely in part but wholly to the Roman supremacy, and that the natural boundary presented by the mighty river was also to become the political boundary. The senate in its better times had not rested, till the dominion of Rome had reached the natural bounds of Italy - the Alps and the Mediterranean - and its adjacent islands. The enlarged empire also needed a similar military rounding off; but the present government left the matter to accident, and sought at most to see, not that the frontiers were capable of defence, but that they should not need to be defended directly by itself. People felt that now another spirit and another arm began to guide the destinies of Rome.

The foundations of the future edifice were laid; but in order to finish the building and completely to secure the recognition of the Roman rule by the Gauls, and that of the Rhine-frontier by the Germans, very much still remained to be done. All central Gaul indeed from the Roman frontier as far up as Chartres and Treves submitted without objection to the new ruler; and on the upper and middle Rhine also no attack was for the present to be apprehended from the Germans. But the northern provinces - as well the Aremorican cantons in Brittany and Normandy as the more powerful confederation of the Belgae - were not affected by the blows directed against central Gaul, and found no occasion to submit to the conqueror of Ariovistus. Moreover, as was already remarked, very close relations subsisted between the Belgae and the Germans over the Rhine, and at the mouth of the Rhine also Germanic tribes made themselves ready to cross the stream. In consequence of this Caesar set out with his army, now increased to eight legions, in the spring of 697 against the Belgic cantons. Mindful of the brave and successful resistance which fifty years before they had with united strength presented to the Cimbri on the borders of their land[38], and stimulated by the patriots who had fled to them in numbers from central Gaul, the confederacy of the Belgae sent their whole first levy - 300,000 armed men under the leadership of Galba the king of the Suessiones - to their southern frontier to receive Caesar there. A single canton alone, that of the powerful Remi (about Rheims) discerned in this invasion of the foreigners an opportunity to shake off the rule which their neighbours the Suessiones exercised over them, and prepared to take up in the north the part which the Haedui had played in central Gaul. The Roman and the Belgic armies arrived in their territory almost at the same time.

Caesar did not venture to give battle to the brave enemy six times as strong; to the north of the Aisne, not far from the modern Pontavert between Rheims and Laon, he pitched his camp on a plateau rendered almost unassailable on all sides partly by the river and by morasses, partly by fosses and redoubts, and contented himself with thwarting by defensive measures the attempts of the Belgae to cross the Aisne and thereby to cut him off from his communications. When he counted on the likelihood that the coalition would speedily collapse under its own weight, he had reckoned rightly. King Galba was an honest man, held in universal respect; but he was not equal to the management of an army of 300,000 men on hostile soil. No progress was made, and provisions began to fail; discontent and dissension began to insinuate themselves into the camp of the confederates. The Bellovaci in particular, equal to the Suessiones in power, and already dissatisfied that the supreme command of the confederate army had not fallen to them, could no longer be detained after news had arrived that the Haedui as allies of the Romans were making preparations to enter the Bellovacic territory.

They determined to break up and go home; though for honour's sake all the cantons at the same time bound themselves to hasten with their united strength to the help of the one first attacked, the miserable dispersion of the confederacy was but miserably palliated by such impracticable stipulations. It was a catastrophe which vividly reminds us of that which occurred almost on the same spot in 1792; and, just as with the campaign in Champagne, the defeat was all the more severe that it took place without a battle.