Riding creatures has not been conceived yet, save for Liffy's marionette horses, but they're marionettes. The best you otherwise have is hain riding white giants for planned travel, but they aren't directed like a horse is. White giants just wander their routes without paying the riders any heed unless they're designated stomp-fodder.

Horse riding would require might at this stage, though. At this stage, people used chariots at best in our equivalent history (at a stretch). It took a while before successful animal trainers were crazy enough to start riding those big, strong, moody, panicky, bucking, skull-cracking, unpredictable creatures known as horses.