Julius Caesar Gallic War 4.19

Caesar, having remained in their territories a few days, and burned all their villages and houses, and cut down their corn, proceeded into the territories of the Ubii; and having promised them his assistance, if they were ever harassed by the Suevi, he learned from them these particulars: that the Suevi, after they had by means of their scouts found that the bridge was being built, had called a council, according to their custom, and sent orders to all parts of their state to remove from the towns and convey their children, wives, and all their possessions into the woods, and that all who could bear arms should assemble in one place; that the place thus chosen was nearly the centre of those regions which the Suevi possessed; that in this spot they had resolved to await the arrival of the Romans, and give them battle there. When Caesar discovered this, having already accomplished all these things on account of which he had resolved to lead his army over, namely, to strike fear into the Germans, take vengeance on the Sigambri, and free the Ubii from the invasion of the Suevi, having spent altogether eighteen days beyond the Rhine , and thinking he had advanced far enough to serve both honor and interest, he returned into Gaul, and cut down the bridge.