Sextus Iulius Frontinus, vir consularis de re militari

Quintus Fabius Maximus, in the Etruscan war, when the ways of scouting were still unknown to Roman leaders, ordered his brother Fabius Caeso, who was skilled in the Etruscan language, to penetrate the Ciminian Forest in Etruscan garb, a forest our soldiers had not dared to enter before. He did this so prudently and industriously that, having crossed the shady forest, he compelled the Camertes to an alliance with the Roman people. The Carthaginians, when they noticed that Alexander's resources were so great that they threatened Africa as well, ordered one of their citizens, a sharp man named Hamilcar Rhodunus, to go to the king under the guise of exile and to use every effort to win his friendship. Once he possessed this, he made his plans known to his fellow citizens. The same Carthaginians sent men who would linger in Rome for a long time under the guise of ambassadors and discover the plans of the Romans. Marcus Cato, in Spain, because he could not discover the plans of the enemy in any other way, ordered three hundred soldiers to make an attack at the same time on the enemy's post and to carry one of them back to the camp unharmed. When tortured, that man confessed all the secrets of his people. Caius Marius, the consul, in the Cimbrian and Teutonic war, sent letters to test the loyalty of the Gauls and Ligurians. The first part of them instructed that the inner parts, which were sealed, should not be opened before a certain time, and he later demanded them back before the appointed day. Because he found them broken open, he understood that hostile things were being plotted. There is another method of exploring by which the commanders themselves, without any outside help, foresee things for themselves. Thus Aemilius Paulus, the consul in the Etruscan war near the town of Colonia, was about to lead his army into the plain. Having watched from afar the multitude of birds that had risen from the forest with a faster flight, he understood that some kind of ambush lay there, because the birds were disturbed and flew out many at once. Therefore, having sent scouts ahead, he discovered that ten thousand Boii were waiting there to catch the Roman column on its march. He sent his legions and surrounded them on a side other than what was expected. Similarly, Thyamenus, son of Orestes, when he heard that a ridge naturally fortified was held by the enemy, sent men ahead to investigate what the situation was. When they reported that it was not true what he had suspected, he began the journey, but when he saw a great force of birds flying out at the same time from the suspected ridge and not settling at all, he thought that an enemy column lay hidden there. Thus, by leading his army around, he eluded the ambushers. Hasdrubal, brother of Hannibal, then understood that the army of Livius and Nero—even though they tried to hide this by not doubling their camps—was there, because he noticed from the march that their horses were thinner and the men were more bronzed, as if from a sea voyage.