C. Julius Caesar, Gallic War

When he had proceeded three days' journey, word was brought to him that Ariovistus was hastening with all his forces to seize on Vesontio , which is the largest town of the Sequani, and had advanced three days' journey from its territories. Caesar thought that he ought to take the greatest precautions lest this should happen, for there was in that town a most ample supply of every thing which was serviceable for war; and so fortified was it by the nature of the ground, as to afford a great facility for protracting the war, inasmuch as the river Doubs almost surrounds the whole town, as though it were traced round it with a pair of compasses. A mountain of great height shuts in the remaining space, which is not more than 600 feet, where the river leaves a gap, in such a manner that the roots of that mountain extend to the river's bank on either side. A wall thrown around it makes a citadel of this [mountain], and connects it with the town. Hither Caesar hastens by forced marches by night and day, and, after having seized the town, stations a garrison there.