Reply #5: I would also consider walking at a rate of 4 miles per hour. -- [View All]

[Tuesday Afternoon]

Horses can travel upwards of thirty (and some, even forty) miles per hour. They cannot sustain this pace for long, though. A horse can gallop a couple of miles at full steam, but the same horse can canter (or lope) much farther. Trotting (either a fast trot or a jog trot) isn't a bad way to travel, but you don't get very far very fast. Faster trotting is tiring to the rider as well because you are posting (rising up and down out of the saddle on alternate beats). Horses can walk all day, with brief rest periods. The condition of the horse can make a difference in endurance. A conditioned horse can do much more than one who isn't. The same is true for diet. A horse who has had all he needs to eat and drink is more likely to be a reliable mount. A horse that isn't in shape is more susceptible to injury as well.

more at link:

http://wwwestra.com/horses/history_travel.htm