Xenophon On the Art of Horsemanship 2

[1]
  We do not think it necessary to give directions ¹ for breaking a colt. For in our states the cavalry are recruited from those who have ample means and take a considerable part in the government. And it is far better for a young man to get himself into condition and when he understands the art of horsemanship to practise riding than to be a horse-breaker; and an older man had far better devote himself to his estate and his friends and affairs of state and of war than spend his time in horse-breaking.

[2] So he who shares my opinion about horse-breaking will, of course, send his colt out. Still he should put in writing what the horse is to know when he is returned, just as when he apprentices his son to a profession. For these articles will serve as notes to remind the horse-breaker of what he must attend to if he is to get his money.

[3]
  Still, care must be taken that the colt is gentle, tractable, and fond of man when he is sent to the horse-breaker. That sort of business is generally done at home through the groom, if he knows how to contrive that hunger and thirst and horseflies are associated by the colt with solitude, while eating and drinking and delivery from irritation come through man’s agency. For in these circumstances a foal is bound not only to like men, but to hanker after them.

[4] One should also handle those parts in which the horse likes most to be cherished, that is to say the hairiest parts and those where the horse has least power of helping himself, if anything worries him.

[5] Let the groom be under orders also to lead him through crowds, and accustom him to all sorts of sights and all sorts of noises. If the colt shies at any of them, he must teach him, by quieting him and without impatience, that there is nothing to be afraid of.

  I think that the directions I have given on the subject of horse-breaking are sufficient for the private person.