Hiero the Tyrant and Other Treatises (Penguin Classics) by Xenophon

against the enemy a commander who knows the region is far better off than one in the opposite situation.
    [7] It is also a cavalry commander’s job to have recruited spies, before the outbreak of war, from citizens of neutral states and from merchants – the latter because every state always welcomes people importing [8] goods. False deserters can occasionally be useful too. However, he should never rely on spies so much that he neglects to post guards; on the contrary, he should constantly be in the same state of readiness as he would be if he had received a report that a hostile force was on its way. After all, in wartime it may very well be difficult for even the most trustworthy spy to get a message through at the critical moment. 1
    [9] The enemy will be less likely to become aware of the cavalry leaving the camp if the order is given by word of mouth rather than by crier or by posted notices. So it is advisable, to help the transmission of the command to move out, to appoint not only leaders for every section of ten, but also leaders for every half section of five, so as to reduce to a minimum the number of people to whom each of these officers [10] has to pass the message. Another function these half-section leaders can perform is to facilitate the extension of the regiment’s line, when it is time for this formation, by deploying the men smoothly in their new posts.
    What about when you need to post guards? I for one always recommend keeping your lookouts and sentries hidden, * because then they can serve a dual purpose: they can ambush the enemy as well asguard their friends. At the same time, their invisibility makes them [11] less vulnerable to a surprise attack and more frightening to the enemy. I mean, knowing that there are guards somewhere, but not knowing exactly where or how many of them there are, not only saps the enemy’s morale, but also inevitably makes every location a source of suspicion. Visible guards, however, show him which places are safe and which are unsafe. Besides, hidden guards create the possibility of [12] posting a few men on patrol out in the open in front of their concealed comrades and trying to lure the enemy into an ambush. Another trick for ensnaring the enemy is sometimes to post guards out in the open
behind
the hidden ones; this can prove just as effective a way of taking the enemy in as the trick I have just mentioned. 2
    It is also a mark of a sensible commander never to take risks, if he [13] can help it, except when it is obvious that he will have the enemy at a disadvantage. Doing the enemy favours should be regarded as a betrayal of one’s side rather than as courage. Another sound principle [14] is always to aim for the weak point of the enemy’s position, even if it is a long way off. After all, pushing yourself to make a great effort is less risky than engaging a superior force. However, if the enemy [15] has managed to come between you and a friendly stronghold, then even if they are the superior force, the right thing to do in this situation is to attack them, either on the flank where your presence has gone unnoticed, or on both flanks at once, because as one of your contingents is retiring, the other one can charge the other flank, throw the enemy into chaos and rescue your friends.
    The value of spies as a means of trying to get information about [16] the enemy has long been recognized, but I am sure that the best plan of all is for the cavalry commander to try to observe the enemy himself, if he can find a safe vantage-point, and watch out for any mistakes they might make. You should send suitable men to pilfer anything [17] that can be stolen and dispatch raiders to seize anything they can make off with. If the enemy is on the march somewhere and a part of his force which is weaker than your own becomes detached or rashly fans out from the main body, you should not let this escape your notice, either; but remember that the hunter must always be stronger than