Not far away from Æduan territory were the Helvetii, who were independent of the rule of Ariovistus, and with them the autonomous party among the Ædui entered into friendly relations in order to secure them as allies against the Germans. The Helvetii were to be persuaded by their leaders to migrate to western Gaul, and it was arranged that, when the whole tribe was slowly passing through the land of the Ædui, there should be a rising against Ariovistus. The Ædui could count on the assistance of the Helvetii, because as future occupants of Gallic territory the immigrants would have no desire to be dependents of the German king. This situation and this program were known to Cæsar before he left Rome, for he was in communication with the pro-Roman party among the Ædui. It was of course his object to frustrate this plan of driving out the Germans without the help of Rome, because it was to his interest that Roman overlordship should take the place of German control. The request of the Helvetii to be allowed to pass peacefully through Roman territory came just in time. It gave Cæsar the opportunity of defending the frontier and strengthening his army. As soon as the Helvetii were refused a passage through the Roman province, they started directly for the land of the Ædui, crossing over the Roman territory, and so they abandoned the fiction of a migration to the west. In the meantime, by the liberal use of money, the pro-Roman party among the Ædui had got the upper hand. Accordingly when the Helvetii, whose rear division had been attacked by Cæsar as they were crossing the Saône, reached the land of their would-be allies, they were treated as enemies by the Ædui, who were now calling on Cæsar for help to resist the invaders. The Helvetii, willing to return, desired to come to terms with the Roman general, but they refused to accept the Roman conditions as to hostages. They started to retrace their steps by following a more northerly course on their return in order to take advantage of the mountainous country, as a protection against an attack on the part of the Romans. Cæsar followed warily; his own troops were indeed strengthened by Æduan cavalry, but these, on the first engagement, had fled before the enemy. It was obvious their loyalty could not be depended upon, and significant, too, that Dumnorix was in command. When an attempt to surround the Helvetii with two Roman legions failed, Cæsar withdrew to Bibracte, the Æduan capital, to replenish his army and probably to prevent the defection of his allies. The Helvetii might now have returned to their old home unmolested, but they were embittered against the Romans, who had shown constant hostility to their movements, whether they advanced or retreated, and they were quite willing to treat with the patriotic party among the Ædui, who asked them now for help against the Romans. They turned back therefore, with the purpose of attacking the Romans as they were marching towards Bibracte.