A summary of On the Noble Bearing of the Horse by Xenophon & The Art of Horsmanship.
On the Noble Bearing of the Horse:
This chapter largely describes how to train a horse to carry himself properly … head high and neck arched, with the body collected and ready underneath the rider.

Xenophon’s first instruction is to avoid pulling with the bit or striking the horse when attempting to achieve this carriage. The rider should instead use the reins lightly to encourage the horse to arch his neck and move freely and gracefully.
Xenophon recommends using two bits, one smooth and one rough.
These bits are intended to be used separately, rather than at the same time like the modern double bit.
Each bit is intended to hang in the horses mouth in such a way that, in order to escape the pressure of it, the horse carries his head in the proper place.
The bits should be jointed in order to have a better effect on the horse’s mouth, and once a horse has achieved the desired carriage, the rider should loosen the rein to reward him.
A properly collected horse should not be given rough or angry signals, but instead gentle ones because he is prepared to move forward in an instant.
Xenophon then describes the means by which a rider can ask a horse to move forward most impressively, that is, by holding him back with the reins but urging him forward with the legs, resulting in the horse lifting his legs high in front of himself.