C. Julius Caesar, Gallic War

On the following day they move their camp from that place; Caesar does the same, and sends forward all his cavalry, to the number of four thousand (which he had drawn together from all parts of the Province and from the Aedui and their allies), to observe toward what parts the enemy are directing their march. These, having too eagerly pursued the enemy's rear, come to a battle with the cavalry of the Helvetii in a disadvantageous place, and a few of our men fall. The Helvetii, elated with this battle, because they had with five hundred horse repulsed so large a body of horse, began to face us more boldly, sometimes too from their rear to provoke our men by an attack. Caesar [however] restrained his men from battle, deeming it sufficient for the present to prevent the enemy from rapine, forage, and depredation. They marched for about fifteen days in such a manner that there was not more than five or six miles between the enemy's rear and our van.