Xenophon, On the Art of Horsemanship
E. C. Marchant, G. W. Bowersock, tr. Constitution of the Athenians., Ed.

So far we have described how to avoid being cheated in buying a colt or a horse, how to avoid spoiling him in usage and how to impart to a horse all the qualities required by a cavalryman for war. It is time perhaps to give directions, in case one has to deal with a horse that is too spirited or too sluggish, for the correct way of managing either. [2]

First, then, it must be realised that spirit in a horse is precisely what anger is in a man. Therefore, just as you are least likely to make a man angry if you neither say nor do anything disagreable to him, so he who abstains from annoying a spirited horse is least likely to rouse his anger. [3] Accordingly, at the moment of mounting, the rider should take care to worry him as little as possible; and when he is mounted, he should let him stand still longer than is otherwise usual, and then direct him to go by the most gentle aids. Then let him begin at a very slow pace and increase the speed with the same gentle help, so that the horse will not be aware of the transition to a quicker motion. [4] Any sudden sign disturbs a spirited horse, just as sudden sights and sounds and sensations disturb a man. It is important to realise that a horse too is flurried by anything sudden. [5] If you want to correct a spirited horse when he is going too fast, do not pull him suddenly, but quietly check him with the bit, soothing him, not forcing him, to a quiet pace. [6] Long rides rather than frequent turnings, calm horses; and quiet ones lasting long soothe and calm a spirited horse and do not excite him. [7] But if anyone supposes that he will calm a horse by frequent riding at a quick pace so as to tire him, his opinion is the opposite of the truth. For in such cases a spirited horse does his utmost to get the upper hand by force, and in his excitement, like an angry man, he often causes many irreparable injuries both to himself and to his rider. [8] One must prevent¹ a high-spirited horse from going at his top speed, and of course, entirely avoid letting him race with another horse; for as a rule the most highly spirited horses are also most eager for victory. [9]

As for bits, the smooth are more suitable than the rough; but if a rough one is used, it should be made to resemble a smooth one by lightness of hand. It is also well to accustom oneself to sit still, especially on a spirited horse, and to touch him as little as possible with anything other than the parts that give us a safe seat by contact. [10]

It should also be known that a horse can be taught to be calm by a chirp with the lips and to be roused by a cluck with the tongue. And if from the first you use with the cluck aids to calm him, and with the chirp aids to rouse him, the horse will learn to rouse himself at the chirp and to calm down at the cluck. [11] Accordingly, if a shout is heard or a trumpet sounds, you must not allow the horse to notice any sign of alarm in you, and must on no account do anything to him to cause him alarm, but as far as possible let him rest in such circumstances, and, if you have the opportunity, bring him his morning or evening meal. [12] But the best advice is not to get an over-spirited horse for war.

As for a sluggish beast, I may be content with the remark that in everything you must do the opposite of what we advise for the treatment of a high-spirited one.