The Haedui, who had hitherto continued vacillating, now made preparations in earnest to join the patriotic party; the body of men, whom Caesar had ordered to Gergovia, had on the march been induced by its officers to declare for the insurgents; at the same time they had begun in the canton itself to plunder and kill the Romans settled there. Caesar, who had gone with two-thirds of the blockading army to meet that corps of the Haedui which was being brought up to Gergovia, had by his sudden appearance recalled it to nominal obedience; but it was more than ever a hollow and fragile relation, the continuance of which had been almost too dearly purchased by the great peril of the two legions left behind in front of Gergovia. For Vercingetorix, rapidly and resolutely availing himself of Caesar's departure, had during his absence made an attack on them, which had wellnigh ended in their being overpowered, and the Roman camp being taken by storm. Caesar's unrivalled celerity alone averted a second catastrophe like that of Aduatuca. Though the Haedui made once more fair promises, it might be foreseen that, if the blockade should still be prolonged without result, they would openly range themselves on the side of the insurgents and would thereby compel Caesar to raise it; for their accession would interrupt the communication between him and Labienus, and expose the latter especially in his isolation to the greatest peril. Caesar was resolved not to let matters come to this pass, but, however painful and even dangerous it was to retire from Gergovia without having accomplished his object, nevertheless, if it must be done, rather to set out immediately and by marching into the canton of the Haedui to prevent at any cost their formal desertion.
Before entering however on this retreat, which was far from agreeable to his quick and confident temperament, he made yet a last attempt to free himself from his painful perplexity by a brilliant success. While the bulk of the garrison of Gergovia was occupied in intrenching the side on which the assault was expected, the Roman general watched his opportunity to surprise another access less conveniently situated but at the moment left bare. In reality the Roman storming columns scaled the camp-wall, and occupied the nearest quarters of the camp; but the whole garrison was already alarmed, and owing to the small distances Caesar found it not advisable to risk the second assault on the city-wall. He gave the signal for retreat; but the foremost legions, carried away by the impetuosity of victory, heard not or did not wish to hear, and pushed forward without halting, up to the city-wall, some even into the city. But masses more and more dense threw themselves in front of the intruders; the foremost fell, the columns stopped; in vain centurions and legionaries fought with the most devoted and heroic courage; the assailants were chased with very considerable loss out of the town and down the hill, where the troops stationed by Caesar in the plain received them and prevented greater mischief. The expected capture of Gergovia had been converted into a defeat, and the considerable loss in killed and wounded - there were counted 700 soldiers that had fallen, including 46 centurions - was the least part of the misfortune suffered.
The imposing position of Caesar in Gaul depended essentially on the halo of victory that surrounded him; and this began to grow pale. The conflicts around Avaricum, Caesar's vain attempts to compel the enemy to fight, the resolute defence of the city and its almost accidental capture by storm bore a stamp different from that of the earlier Celtic wars, and had strengthened rather than impaired the confidence of the Celts in themselves and their leader.
Moreover, the new system of warfare - the making head against the enemy in intrenched camps under the protection of fortresses - had completely approved itself at Lutetia as well as at Gergovia. Lastly, this defeat, the first which Caesar in person had suffered from the Celts crowned their success, and it accordingly gave as it were the signal for a second outbreak of the insurrection.
The Haedui now broke formally with Caesar and entered into union with Vercingetorix. Their contingent, which was still with Caesar's army, not only deserted from it, but also took occasion to carry off the depots of the army of Caesar at Noviodunum on the Loire, whereby the chests and magazines, a number of remount-horses, and all the hostages furnished to Caesar, fell into the hands of the insurgents. It was of at least equal importance, that on this news the Belgae, who had hitherto kept aloof from the whole movement, began to bestir themselves. The powerful canton of the Bellovaci rose with the view of attacking in the rear the corps of Labienus, while it confronted at Lutetia the levy of the surrounding cantons of central Gaul.
Everywhere else too men were taking to arms; the strength of patriotic enthusiasm carried along with it even the most decided and most favoured partisans of Rome, such as Commius king of the Atrebates, who on account of his faithful services had received from the Romans important privileges for his community and the hegemony over the Morini. The threads of the insurrection ramified even into the old Roman province: they cherished the hope, perhaps not without ground, of inducing the Allobroges themselves to take arms against the Romans. With the single exception of the Remi and of the districts - dependent immediately on the Remi - of the Suessiones, Leuci, and Lingones, whose peculiar isolation was not affected even amidst this general enthusiasm, the whole Celtic nation from the Pyrenees to the Rhine was now in reality, for the first and for the last time, in arms for its freedom and nationality; whereas, singularly enough, the whole German communities, who in the former struggles had held the foremost rank, kept aloof. In fact, the Treveri, and as it would seem the Menapii also, were prevented by their feuds with the Germans from taking an active part in the national war.
It was a grave and decisive moment, when after the retreat from Gergovia and the loss of Noviodunum a council of war was held in Caesar's headquarters regarding the measures now to be adopted. Various voices expressed themselves in favour of a retreat over the Cevennes into the old Roman province, which now lay open on all sides to the insurrection and certainly was in urgent need of the legions that had been sent from Rome primarily for its protection. But Caesar rejected this timid strategy suggested not by the position of affairs, but by government-instructions and fear of responsibility. He contented himself with calling the general levy of the Romans settled in the province to arms, and having the frontiers guarded by that levy to the best of its ability. On the other hand he himself set out in the opposite direction and advanced by forced marches to Agedincum, to which he ordered Labienus to retreat in all haste. The Celts naturally endeavoured to prevent the junction of the two Roman armies. Labienus might by crossing the Marne and marching down the right bank of the Seine have reached Agedincum, where he had left his reserve and his baggage; but he preferred not to allow the Celts again to behold the retreat of Roman troops. He therefore instead of crossing the Marne crossed the Seine under the eyes of the deluded enemy, and on its left bank fought a battle with the hostile forces, in which he conquered, and among many others the Celtic general himself, the old Camulogenus, was left on the field. Nor were the insurgents more successful in detaining Caesar on the Loire; Caesar gave them no time to assemble larger masses there, and without difficulty dispersed the militia of the Haedui, which alone he found at that point