Although the fire prevented Cæsar from seeing the retreat of the enemy, he suspected it. He ordered his legions to advance, and sent the cavalry in pursuit; but he marched only slowly, for fear of some stratagem, as the barbarians might have formed the design of drawing the Romans to a disadvantageous ground. Besides, the cavalry did not dare to ride through the smoke and flames; and thus the Bellovaci were able to pass over a distance of ten miles, and halt in a place strongly fortified by nature, Mont Ganelon, where they pitched their camp. In this position, they confined themselves to placing cavalry and infantry in frequent ambuscades, thus inflicting great damage on the Romans when they went to forage.[546] [Sidenote: Battle on the Aisne.] III. After several encounters of this kind, Cæsar learnt by a prisoner that Correus, chief of the Bellovaci, with 6,000 picked infantry and 1,000 horsemen, were preparing an ambuscade in the places where the abundance of corn and forage was likely to attract the Romans. In consequence of this information, he sent forward the cavalry, which was always employed to protect the foragers, and joined with them some light-armed auxiliaries; and he himself, with a greater number of legions, followed them as near as possible. The enemy had posted themselves in a plain (that of Choisy-au-Bac) of about 1,000 paces wide in every direction, and surrounded on one side by forests, on the other by a river which was difficult to pass (the Aisne). The cavalry were acquainted with the designs of the Gauls; feeling themselves supported, they advanced resolutely, in squadrons, towards this plain, which was surrounded with ambushes on all sides. Correus, seeing them arrive in this manner, believed the opportunity favourable for the execution of his plan, and began by attacking the first squadrons with a few men. The Romans sustained the shock, without concentrating themselves in a mass on the same point, “which,” says Hirtius, “happens usually in cavalry engagements, and leads always to a dangerous confusion.” There, on the contrary, the squadrons remained separated, fought in detached bodies, and, when one of them advanced, its flanks were protected by the others. Correus then ordered the rest of his cavalry to issue from the woods. An obstinate combat began on all sides, without any decisive result, until the enemy’s infantry, debouching from the forest in close ranks, forced the Roman cavalry to fall back. The lightly-armed soldiers, who preceded the legions, placed themselves between the squadrons, and restored the fortune of the combat. After a certain time, the troops, animated by the approach of the legions and the arrival of Cæsar, and ambitious of obtaining alone the honour of the victory, redoubled their efforts, and gained the advantage. The enemies, on the other hand, were discouraged and took to flight; but they were stopped by the very obstacles which they intended to throw in the way of the Romans.