An averagely fit horse can travel maybe ten miles further than an averagely fit person in a day. But not as far if you expect them to maintain a pace faster than a person, with a person and belongings on their back.
At the limits of our endurance, human ultra-runners perform about as well as horses over very long distances in terms of simple endurance — carrying our own weight without stopping. It’s only over short distances that horses have such obvious advantages.
If you had a horse and you needed to cover great distance, you spent as much of that time as you could doing your own walking.