Even writers who have zero interest in horses, if they’re writing in a setting that features equines at all, can be persuaded to take an interest in the clothes people wear on and around the big scary animals. The history of riding apparel is long, varied, and full of bizarre fashion statements, but at base it is, and must be, functional. Whatever the color, cut, or ornamentation, the outfit has to work for its living, and that means certain essential requirements have to be met.
First of all, horses are large, can be clumsy, and one of those hooves lands on your foot, you know it. So, the rider’s outfit begins with a pair of good, sturdy shoes or boots. Cowboy boots evolved their familiar shape for solid functional reasons. The narrow toes fit easily into the stirrups, but the heels keep the foot from sliding all the way through and getting caught, which can be catastrophic if the horse throws you (getting dragged is not good for any part of the draggee). Most stirrup-using cultures feature a riding boot with some kind of heel, for the rider’s safety. Cultures without stirrups don’t suffer from those restrictions, though bare feet or sandals don’t mix well with horses’ hooves.
The riding boot will tend to be at least ankle height for functional reasons. Slippers or sneakers can come off, but a boot or shoe that goes up past the ankle will tend to stay on. It also supports the ankle and gives the rider more oomph in use the leg to direct the horse. If the rider wears spurs–and a cowboy may wear a highly ornamented set, much like a medieval knight–the boot offers a secure surface to strap the spurs to.
English riding boots–the familiar tall black (or brown) stovepipe style that goes in and out of street fashion–perform a similar function. The stiff, tall leg of the boot goes along with the style of riding, which relies quite a bit on application of the lower leg for direction and stability. The heel is relatively small–half an inch or so–in keeping with the restraint of the overall attire. A modern variation, now even show-legal, is a set of paddock shoes (old-fashioned leather lace-up or pull-on ankle boots) and a pair of half chaps or gaiters–leather or suede leg wraps that slip on over the shoes, are held in place at the bottom by a strap, and zip, button, or velcro up the leg to the knee. The full version of this, the cowboy’s chaps, not only protects his tender bits from the rubbing of the saddle, but also guards his legs against weather, spiny vegetation, and animal attack.
What the rider wears above the boots will vary widely according to taste and discipline, but again, form arises from function. The long, flowing skirt of the old-style riding habit is beautiful and elegant, but it also provides the rider’s legs with full coverage, and is unlikely to flip up at she clears a fence or rides a good gallop. Very important for modesty, that. The heavy fabric serves as padding, because if there’s one thing riding is about, it’s friction. You need a degree of it to stay in the saddle, but beyond a certain point, well, ow.
Those who ride astride will default to trousers of some sort fairly quickly–witness the ancient Scythians and Persians, though the Greeks clung to their tunics with masochistic persistence. The first place a pair of riding pants will wear out is the seat and crotch. Then the knees. Leather breeches, sweat factor aside, make sense in terms of durability. Modern versions have leather seats (deerskin for choice) and fabric everything else, which is a good compromise.
Jeans made the old way, with solid stitching and rivets, were originally designed to ride in. The inside seams can rub ferociously, but that can be got around by going to flat seams. If the jeans are too tight, like any other riding pants, they will split–and in an embarrassing location, too. Modern stretch jeans get around this, as do the many variations of English riding breeches and tights (yes, even men will ride in tights). In older settings, looser cut especially in the crotch and seat allows for the rider’s need to move freely in the saddle.
The rest of the outfit has a lot more scope for variation, since it’s not in direct contact with the horse. Strictly functional shirts, tunics, jackets, doublets, etc. will have a minimum of moving parts and dangling bits, though ceremonial outfits can pull out every possible stop. Like, for example, this. That’s the American interpretation of Arab “native” costume, i.e. bells, dangles, and tassels galore. And then there’s this: modern Western show costume, in which one’s love of sequins, glitter, and bling get to show themselves off–coordinated, of course, with the horse’s coat color and accessories.
Even the relative simplicity of English riding gear has its moments. High-level riders in dressage and eventing will show up in top hats and tails–and although a wild color statement is a navy coat or a set of lavender points on the waistcoat, the rider might sneak in a few discreet colored crystals on the stirrups or the horse’s headstall. You really can’t keep the human love of shiny things down.
And finally, of course, headgear. Culture and fashion will determine what a rider wears on his or her head, from a ten-gallon hat to a formal top hat to an Eastern turban. Modern obsession with safety means that in the US and in parts of Europe especially, riders wear a variation on the design of a bicycle helmet, designed to protect the cranium from a fall from a much greater height and with correspondingly greater force. Originally worn by race jockeys and cross-country jumpers, the safety helmet has slowly crept through the discplines, so that there’s even a version that fits under a cowboy hat–though the top hats and derbies of the show riders remain determinedly un-safety-fied.