C. Julius Caesar, Gallic War

At the same time, Caius Fabius, a lieutenant, brings back many states to their allegiance, and confirms their submission by taking hostages; he was then informed by letters from Caninius, of the proceedings among the Pictones. Upon which he set off to bring assistance to Duracius. But Dumnacus, hearing of the approach of Fabius, and despairing of safety, if at the same time he should be forced to withstand the Roman army without, and observe, and be under apprehension from the town's people, made a precipitate retreat from that place with all his forces. Nor did he think that he should be sufficiently secure from danger, unless he led his army across the Loire , which was too deep a river to pass except by a bridge. Though Fabius had not yet come within sight of the enemy, nor joined Caninius; yet being informed of the nature of the country, by persons acquainted with it, he judged it most likely that the enemy would take that way, which he found they did take. He therefore marched to that bridge with his army, and ordered his cavalry to advance no farther before the legions than that they could return to the same camp at night, without fatiguing their horses. Our horse pursued according to orders, and fell upon Dumnacus's rear and attacking them on their march, while fleeing, dismayed, and laden with baggage, they slew a great number, and took a rich booty. Having executed the affair so successfully, they retired to the camp.