Sextus Iulius Frontinus, vir consularis de re militari

...the war was accomplished immediately. Caesar, about to fight against the Germans and Ariovistus, when the spirits of his men were confused, said in an assembly that he would use the services of no one that day except the tenth legion. By this, he achieved that the tenth, as if by a testimony of special bravery, was forced to act, and the others were ashamed that the glory of virtue would be in the hands of others. Q. Fabius, who excellently knew that the Romans were of that liberty which would be exasperated by insult and expected nothing just or moderate from punishments, sent legates to Carthage about the conditions of peace. When they reported that these were full of iniquity and insolence, the Roman army was incited to fight. Agesilaus, the leader of the Lacedaemonians, when he had his camp near the city of Orchomenus and discovered that most of the soldiers were depositing their most valuable things within the fortifications, commanded the townspeople that nothing pertaining to his army should be received, so that the soldiers would fight more ardently, knowing that they had to fight for all their own belongings. Epaminondas, the leader of the Thebans, about to fight against the Lacedaemonians, so that his soldiers would be assisted not only by their strength but also by their passions, announced in an assembly that it was determined for the Lacedaemonians, if they gained the victory, to kill all of the male sex and, having led their wives and children into slavery, to destroy Thebes. Excited by this assembly, the Thebans overcame the Lacedaemonians in the first charge. Eutidas, leader of the Lacedaemonians, about to fight on the same day that his allies had won with the fleet, although ignorant of the act, spread the news that victory had been gained by his side so that he would have soldiers more constant for the battle. Aulus Postumius, in the battle in which he fought with the Latins, raised the spirits of his men by offering the appearance of two youths on horses, saying that Pollux was present, and thus he restored the battle. Archidamus the Lacedaemonian, waging war against the Arcadians, set weapons in the camp and secretly ordered horses to be led around them at night. By showing their tracks in the morning as if Castor and Pollux had ridden by, he persuaded them that the same would be present for them fighting. Pericles, the leader of the Athenians, about to enter battle, when he had noticed a grove from which both lines could be seen—a place of immense opacity and otherwise sacred to the rich Father—he placed a man of huge stature in a chariot of white horses, dressed in very high buskins and a purple garment, venerable in appearance, who, at the given sign of battle, would ride forward and, calling Pericles by voice, would encourage him and say that the gods of the Athenians were present.