Julius Caesar Gallic War 4.16

The German war being finished, Caesar thought it expedient for him to cross the Rhine , for many reasons; of which this was the most weighty, that, since he saw the Germans were so easily urged to go into Gaul, he desired they should have their fears for their own territories, when they discovered that the army of the Roman people both could and dared pass the Rhine . There was added also, that portion of the cavalry of the Usipetes and the Tenchtheri, which I have above related to have crossed the Meuse for the purpose of plundering and procuring forage, and was not present at the engagement, had betaken themselves, after the retreat of their countrymen, across the Rhine into the territories of the Sigambri, and united themselves to them. When Caesar sent embassadors to them, to demand that they should give up to him those who had made war against him and against Gaul, they replied, "That the Rhine bounded the empire of the Roman people; if he did not think it just for the Germans to pass over into Gaul against his consent, why did he claim that any thing beyond the Rhine should be subject to his dominion or power?" The Ubii, also, who alone, out of all the nations lying beyond the Rhine , had sent embassadors to Caesar, and formed an alliance and given hostages, earnestly entreated "that he would bring them assistance, because they were grievously oppressed by the Suevi; or, if he was prevented from doing so by the business of the commonwealth, he would at least transport his army over the Rhine ; that that would be sufficient for their present assistance and their hope for the future; that so great was the name and the reputation of his army, even among the most remote nations of the Germans, arising from the defeat of Ariovistus and this last battle which was fought, that they might be safe under the fame and friendship of the Roman people." They promised a large number of ships for transporting the army.