C. Julius Caesar, Gallic War

Caesar at first determined to decline a battle, as well on account of the great number of the enemy as their distinguished reputation for valor: daily, however, in cavalry actions, he strove to ascertain by frequent trials, what the enemy could effect by their prowess and what our men would dare. When he perceived that our men were not inferior, as the place before the camp was naturally convenient and suitable for marshaling an army (since the hill where the camp was pitched, rising gradually from the plain, extended forward in breadth as far as the space which the marshaled army could occupy, and had steep declines of its side in either direction, and gently sloping in front gradually sank to the plain); on either side of that hill he drew a cross trench of about four hundred paces, and at the extremities of that trench built forts, and placed there his military engines, lest, after he had marshaled his army, the enemy, since they were so powerful in point of number, should be able to surround his men in the flank, while fighting. After doing this, and leaving in the camp the two legions which he had last raised, that, if there should be any occasion, they might be brought as a reserve, he formed the other six legions in order of battle before the camp. The enemy, likewise, had drawn up their forces which they had brought out of the camp.