He had been nominally a sort of ally of the Romans.

He had extended his conquests across the Rhine into Gaul, and he held some nations there as his tributaries.

Among these, the Aeduans were a prominent party, and, to simplify the account, we will take their name as the representative of all who were concerned.

When Caesar came into the region of the Aeduans, he entered into some negotiations with them, in which they, as he alleges, asked his assistance to enable them to throw off the dominion of their German enemy.

It is probable, in fact, that there was some proposition of this kind from them, for Caesar had abundant means of inducing them to make it, if he was disposed, and the receiving of such a communication furnished the most obvious and plausible pretext to authorize and justify his interposition.
Caesar accordingly sent a messenger across the Rhine to Ariovistus, saying that he wished to have an interview with him on business of importance, and asking him to name a time which would be convenient to him for the interview, and also to appoint some place in Gaul where he would attend.
[Sidenote: Caesar's negotiations with Ariovistus.] To this Ariovistus replied, that if he had, himself, any business with Caesar, he would have waited upon him to propose it; and, in the same manner, if Caesar wished to see him, he must come into his own dominions.