Polyænus also teaches the necessity of "psychologising"—a term not unknown to American experts in that form of police torture which is known as the Third Degree—the leader to whom one may be opposed. "One must exert oneself," says the Greek, "to find out the character of one's enemy as well as his disposition; whether he is impetuous and spirited at the first shock, or patient and apt to await the onslaught." Every general should know all there is to be known about the business of opponents, and he goes on to tell the tale in point, showing that what we know to-day as the Black Cabinet—that is, the spying of private correspondence in the post—was practised by Alexander the Great who lived some three hundred years before Christ. "Being in Carmania, he was informed that the Macedonians and Greeks in his army were speaking badly about him. Alexander thereupon assembled his friends and told them that as he intended writing home they should do likewise. Accordingly, they all wrote home and Alexander saw to it that the couriers were recalled with the mails before they had gone very far on their journey." Recurring to the same authority, we learn that cipher was well known to the Greeks under the name _skutate_ and to the Romans as _scutula_, meaning a wooden cylinder around which an inscribed papyrus was rolled. He also records the story of Histiæus, a tyrant of Miletus who wished to incite Ionia to rebel against Darius; fearing however to send letters to the Ionians in those perilous times, he thought out the ruse of having the head of a trusted slave clean shaved and a message written on the scalp, addressed to Aristagoras in the simple words: "Rouse Ionia to revolt." The slave was then sent on his way to Ionia, and, his hair having grown over the fateful message by the time hostile camps were reached, he passed safely through to Aristagoras, who had the poll shaved once more and so learned his general's design. Altogether it would seem that during antiquity, ruse rather than real ability was the cause of many loud-famed successes and victories. Frontinus tells how the Consul Hirtius used to send carrier-pigeons to his friend Decimus Brutus, and Justus Lipsius is responsible for the statement that swallows were trained for purposes of military and other espionage, the same authority informing us that it was the custom among Eastern nations for birds to be trained as long-distance messengers, more especially between lovers. It may be certain, too, that postal communications were not all entrusted to the famous relay runners, regarding whose marvellous stamina the Roman records tell us.