Julius Caesar Gallic War 3.1

When Caesar was setting out for Italy, he sent Servius Galba with the twelfth legion and part of the cavalry, against the Nantuates, the Veragri, and Seduni, who extend from the territories of the Allobroges, and the lake of Geneva , and the River Rhone to the top of the Alps. The reason for sending him was, that he desired that the pass along the Alps , through which [the Roman] merchants had been accustomed to travel with great danger, and under great imposts, should be opened. He permitted him, if he thought it necessary, to station the legion in these places, for the purpose of wintering. Galba having fought some successful battles and stormed several of their forts, upon embassadors being sent to him from all parts and hostages given and a peace concluded, determined to station two cohorts among the Nantuates, and to winter in person with the other cohorts of that legion in a village of the Veragri, which is called Octodurus; and this village being situated in a valley, with a small plain annexed to it, is bounded on all sides by very high mountains. As this village was divided into two parts by a river, he granted one part of it to the Gauls, and assigned the other, which had been left by them unoccupied, to the cohorts to winter in. He fortified this [latter] part with a rampart and a ditch.