C. Julius Caesar, Gallic War

When each army was in sight of the other, and was pitching their camp almost opposite that of the enemy, scouts being distributed in every quarter, lest the Romans should build a bridge and bring over their troops; it was to Caesar a matter attended with great difficulties, lest he should be hindered from passing the river during the greater part of the summer, as the Allier can not generally be forded before the autumn. Therefore, that this might not happen, having pitched his camp in a woody place opposite to one of those bridges which Vercingetorix had taken care should be broken down, the next day he stopped behind with two legions in a secret place; he sent on the rest of the forces as usual, with all the baggage, after having selected some cohorts, that the number of the legions might appear to be complete. Having ordered these to advance as far as they could, when now, from the time of day, he conjectured they had come to an encampment, he began to rebuild the bridge on the same piles, the lower part of which remained entire. Having quickly finished the work and led his legions across, he selected a fit place for a camp, and recalled the rest of his troops. Vercingetorix, on ascertaining this fact, went before him by forced marches, in order that he might not be compelled to come to an action against his will.