§1. Most men love treachery but hate traitors.
I call those men traitors who secretly surrender their homeland, prince, army, secrets, or other things to the enemy, or who share counsels with enemies for the destruction of those to whom they owe fidelity. Accordingly, those who open gates or bring about something advantageous to the enemy are called by this name. Those, however, who come from the enemy, secretly insinuate themselves, and employ fraud are not traitors. Indeed, in a just war this is a stratagem, not treachery. Such are those who secretly approach enemy places in rustic dress and by other means; they are scouts rather than traitors.
§2. Men frequently employ feigned treachery in order to draw into destruction those who know how to solicit the minds of soldiers; and thus even traitors are not easily trusted. Alcibiades, employing a fugitive, persuaded the Syracusans to leave the city, which he himself soon captured. He had an army at Catana. A fugitive asserted that the Catanians wished to crush the Greeks and could do so if they received assistance from the Syracusans. The Syracusans went to Catana with all their forces, and Alcibiades captured Syracuse undefended.
The Romans were too credulous. When they were going to free Piso, who was besieged in a tower, they heard from a fugitive the report which Mago had cunningly spread: that Piso had been captured. Terrified, they withdrew.
Guido of Friuli, while besieged, arranged that some citizens should bring certain enemies into the city through feigned treachery. He himself went out by another gate and cut down those who were outside and unprepared; then, returning, he killed or captured those who were wandering through the city intent upon plunder.
§3. When Frederick, king of Aragon, did not know in what place Robert of Naples was going to invade Sicily, he commanded certain citizens of Trapani to persuade Robert to besiege Trapani. As it happened, Frederick himself placed a garrison in it and compelled Robert to remain there throughout the summer, and even to make peace as winter approached.
Mentor, sending letters under the seal of the defeated Hermias, occupied many cities. Frederick, count of Ferrara, sent letters to the commander of Varrueal after imitating Sigismund’s hand; he asked whether the commander required a garrison, and, when the latter answered affirmatively, Frederick sent his own.
§4. Care must be taken in various ways that credit be taken away from deserters; for this both restrains desertions, prevents the enemy from learning your plans, and punishes traitors. Hannibal took credit away from deserters. For when he knew that scouts of the Romans were in his camp, he publicly denied that his soldiers who had deserted to the Romans should be called deserters, since they were most skillful soldiers who, at his command, were gathering the enemy’s plans. Hannibal was believed, and the genuine deserters, regarded as scouts, were sent back with their hands cut off.
It belongs to a good commander to conceal matters not only from the enemy but even from his own soldier and to deceive him. When Marcus Licinius Crassus was asked at what time he was going to move camp, he replied: “Are you afraid that you will not hear the trumpet?” With a similar plan Furius, having been cast into an unfavorable place, feigned hope in his expression and led the column around, bringing men ignorant of the danger out of it. Claudius Nero’s deed was bold and then too hazardous: he kept Hannibal ignorant of it until he had killed Hasdrubal. Mithridates remained hidden from Pompey while passing by his camp. When Hamilcar was seeking Sicily, he gave out tablets which were not to be read unless the ships wandered away from the admiral’s ship.
§5. Meanwhile, to use traitors also for concealing plans and to turn them to one’s own use belongs to an industrious commander. Frontinus says in book 1, chapter 1:
“In the Parthian War against King Pacorus, Ventidius was not ignorant that a certain Pharnaeus, a Cyrrhestian by nation, one of those who seemed to be allies, was reporting to the Parthians everything that was being done among his own men. He turned the barbarian’s perfidy to his own advantage. For he pretended to fear that those things which he especially desired to happen might happen, and to desire that those things which he feared might happen. Therefore, anxious lest the Parthians cross the Euphrates before the legions which he had beyond the Taurus in Cappadocia came to him, he carefully worked upon the traitor so that, with his customary perfidy, he would persuade the Parthians to convey their army across by Zeugma, where the route is shortest and the Euphrates flows in a confined channel. For he asserted that if they came that way he would use the advantage of the hills to elude the archers; but that he feared everything if they advanced into open plains.
“Induced by this assertion, the barbarians led their army around by the lower route. While they joined the more widely spread banks with bridges, which were for this reason more laborious, and constructed the apparatus, they spent more than forty days. Ventidius used this interval to gather his forces; and, having received them three days before the Parthian arrived, he joined battle, conquered the Parthians, and killed Pacorus.”
That opportunity is never lacking, especially when wars are among neighbors. Therefore a commander ought to institute now one thing, now another, so that he may deceive the enemy; nor is there any doubt that those who seek a reward from the other side will report it.
The deed of Titus Didius was also prudent. Distrusting the small number of his own men, when he had decided to prolong the war until the arrival of those legions which he expected and had discovered that the enemy was proceeding to meet them, Didius called an assembly and ordered the soldiers to be made ready for battle. He deliberately commanded that the prisoners be guarded rather negligently. A few of them escaped and announced to their own men that a battle was imminent. But the enemy, from suspicion of battle and lest they divide their forces, omitted to intercept those for whom they had been lying in wait. The legions reached Didius in complete safety, with no one intercepting them. Frontinus, book 1, chapter 8.