Res Gestae

Then, after long conference with the men of highest rank, Gratian thought it dangerous and fruitless to struggle with untimely obstinacy against rugged jutting heights; opinions varied greatly, as was natural in such circumstances, but it was finally decided that, with the soldiers at rest, the barbarians should be shut in on all sides and exhausted by famine, since they were protected by the unevenness of the ground.

But when the Germans resisted with the same persistence, and, being acquainted with the country, made for other mountains, higher than those which they had occupied before, the emperor wheeled in that direction with his army, and with the same courage as before sought to find paths leading to the heights.