Before most of the world woke up this morning, 47 riders from around the globe had saddled half-wild horses and set out on what the Guinness Book of World Records has called the longest equestrian race on Earth.

The goal—beyond not getting seriously injured—is to ride a 621-mile circuit (1,000 kilometers) of Mongolian steppe in less than ten days.

Fewer than half of the riders are expected to make it across the finish line. The rest will either quit or be carried off the course by the medical team. Broken bones and torn ligaments are common, frustration and bruised egos the norm. Every rider will fall off multiple times during the course of the race, says Katy Willings, the race chief and a former Mongol Derby competitor.

The race route is modeled on the horse relay postal system created under Genghis Khan in 1224, which was instrumental in the expansion of the Mongolian Empire. Guided by a local escort, specially appointed postal riders would gallop more than 100 miles (160 kilometers) to a morin urtuu, or horse relay station, where another escort would be waiting with a fresh horse.

At the postal route's zenith, a letter could cross from Kharkhorin in the east to the Caspian Sea on the far western edge of the empire, a distance of some 4,225 miles (6,800 kilometers), in two weeks (an average of about 300 miles, or 480 kilometers, a day). Postal riders continued to deliver the mail until 1949, when the Soviet Union—which then controlled Mongolia—shut down the system in an attempt to erase the history of Genghis Khan from the country.

"The horse stations were not permanent but rather a responsibility that rotated so that each family provided the compulsory service for a month each year or two," explains Dandar Gongor, 86, a former escort. From the age of 12 to 15, he carried the riders' mailbags while navigating them to the next horse station.

"You would meet all sorts of people," he says, referring to the postal riders. "Some were kind and would tell you folk stories while you rode. Others were arrogant and mean. We would let the next urtuu supervisor know what kind of people they were, and this would help him decide if [the postal rider] would be given a well-behaved or difficult horse."

View Images Derby riders stop to water their horses as a storm rolls in. The competitors are completely exposed to the elements for the duration of the Derby and over 10 days will likely face extremes of temperature, storms, high winds, and blistering sun. Photograph by Anya Campbell, The Adventurists

Race Logistics

According to the Adventurists, the United Kingdom-based company that created the race in 2009, the course changes about 25 percent from year to year. One of the main concerns is ensuring there are enough reliable water sources along the route.

Would-be competitors submit a written application and are interviewed by phone. There is a $13,122 (U.S.) race fee, which covers the cost of the horses, medical and veterinary support, GPS and tracking devices for each rider, interpreters, vehicles, and pre-race training.

Aside from selecting the riders, the Adventurists also take care in choosing each individual horse for the race. The Mongol herders have introduced the horses to the feel of a bridle and saddle, but the animals are far from broken and are quick to buck or bolt.

View Images When not racing, the horses are cared for by the local herding families who staff much of the Mongol Derby course. The horses are also monitored by a team of veterinarians during the event. Photograph by Quentin Moreau, The Adventurists

This year more than a thousand horses were needed. The herders who own the horses are paid for each horse they supply. The Adventurists declined to answer how much each herder is paid per horse but claim that these payments are "a massive part of the families' general income."

A few days before the race, the riders are required to attend a pre-Derby training session where their abilities are assessed by Western and Mongolian equestrian experts. The riders also receive a detailed map of the area, a GPS, and a spot tracker, which is required to be attached to their person rather than to their horse in case they are thrown.

The spot tracker lets race officials know where each rider is at all times in case of emergencies and allows race watchers to follow the competitors' progress online. Each GPS is programmed with the coordinates for each of the 25 horse stations, which are spread 25 miles (40 kilometers) apart.

It is much more a mental challenge than it is a physical one.

Riders must stop at each station and switch horses to prevent injury or exhaustion of their mounts. "This is not an endurance race for the horses," explains Willings. And just like in Genghis Khan's time, local Mongolian families manage each urtuu, providing food and sleeping arrangements for the riders.

Further complicating the challenge, the widely varied Mongolian landscape is difficult to prepare for: high passes, wooded hills, river crossings, wetlands and floodplains, sandy semiarid dunes, rolling hills, and dry riverbeds, as well as the famous wide-open grasslands. Of course, all of this terrain is navigated while adjusting to the erratic temperaments of a new semiwild horse every 25 miles.

It is much more a mental challenge than it is a physical one, Willings says. "I think anyone can cope with anything for a weekend," she says, "but over ten days, you get buffeted by good and bad fortune a lot."

View Images Fresh horses await their incoming riders at one of the horse relay stations, which are spaced at roughly 25-mile (40 kilometer) intervals. When stopping to change horses, riders can also rest and eat. Photograph by Charles van Wyk, The Adventurists

Horse Welfare

Though the riders are allowed to abuse their own bodies in any way they see fit, the Adventurists take extra precautions to ensure the safety of the horses. Before the competition begins, the riders are weighed wearing their riding clothes, an empty pack, and an empty water container, while holding their Mongolian saddle and bridle; in total they cannot weigh more than 187 pounds (85 kilograms). They are allowed an additional 11 pounds (5 kilograms) in their packs after being weighed.

When a horse and rider arrive at an urtuu, a veterinarian will check the horse's metabolic conditions, hydration, physical soundness, and heart rate. The Mongol Derby uses the endurance heart rate standard of the Fédération Equestre Internationale, the governing body of equestrian sports, which mandates that a horse's heart rate must return to no more than 64 beats per minute within 30 minutes of stopping. If the horse's heart rate does not return to 64 bpm by this time, the rider receives a two-hour penalty.

Race organizers take these rules seriously. Last year, the rider who crossed the finish line first was penalized two hours because her horse's heart rate didn't return to the 64 beats maximum in the allotted time, and the second rider to finish—Lara Prior-Palmer—ended up with the winning time.

These kinds of rules force the riders to keep their horses' welfare first. "The race is based on Genghis Khan's idea, but our execution is much more modern and, dare I say, a bit more responsible," says Willings.

View Images Competitors ride Mongol horses, one of the species’ smallest but hardiest breeds. Mongolian warriors rode these horses to conquer a kingdom stretching from Beijing to Moscow to Baghdad. Photograph by Anya Campbell, The Adventurists

The Competitors

Though the horses are generally no worse for the wear after the race, the same cannot be said for the riders. "Oh, there have been broken bones, torn ligaments, a broken pelvis, a punctured lung, broken collarbones, lots of ribs ... and once a neck," says Willings.

But more riders are signing up every year. Last year, Prior-Palmer, a 19-year-old British rider, won the race in seven days, making her the first female rider to win the Mongol Derby. This year's field includes riders from 16 countries, including Germany, Switzerland, Australia, the U.S., the U.K., Iceland, China, and Ireland.

Rose Sandler, a 32-year-old biochemical engineer from Pipersville, Virginia, has been preparing for the past four months. She was a last-minute addition to the competition when a place opened up unexpectedly. "I've been told that it breaks you down to the basics of human existence," she says.

I'm in it to win it, but not at the exclusion of enjoying everything else about it.

From the moment she was given a spot in the race, Sandler has been talking with past Mongol Derby riders, training with her gear, and honing her strategy. "I'm in it to win it, but not at the exclusion of enjoying everything else about it," she says.

Sandler has been meticulous to the last pound about what to include in her pack: backup batteries for the GPS and spot tracker, a camera, fruit, medical supplies, water purification drops, electrolytes, sleeping bag, down jacket, raincoat shell, extra socks, super glue, two different kinds of antibiotics, zip ties, and protein bars.

Sandler says the best advice she was given was to listen to the herders. "I've been told that if the herders tell you not to take a horse that you want to take or if the herders suggest that you take a specific horse, you should probably listen to them because they know the horses."

View Images Mongolia is home to one of the world's oldest equestrian cultures. Stallions, like this palomino, are especially revered, and their manes are never cut. Photograph by Anya Campbell, The Adventurists

Another rider, Per Michanek, a 59-year-old Swedish equine veterinarian, has a different approach. "I'm going to try [to win], but it's not really that important," says Michanek. "I want to finish."

Much more relaxed in his preparation for the race, he has been trying to ride 62 miles (100 kilometers) every day, "just to know what it's like." He has been riding every day for the past 40 years and believes that accumulated experience is enough to get him through the race.

His gear: an inflatable mattress, light waterproof clothes, storm lighter, paracord, multi-tool, sewing kit, antichafing plasters, presents for Mongolian kids, video camera, batteries, emergency beacon, solar charger, mosquito repellant, pipe and tobacco, heart-rate monitor, wet wipes, toothbrush, soap, razor, and flashlight.

He is purposely not packing food, thinking it a waste of precious space. However, he is packing a ukulele because "if you can't speak with the Mongolians, you can at least sing with them."

Michanek is concerned he is at a disadvantage compared with the female riders. "I think it's very difficult to win as a man because the girls weigh less," he says. And although he is older than most competitors, he has hope: "I've ridden horses all my life, and basically it's the horses that do the job."

View Images The U.K.'s Lara Prior-Palmer rides the last leg of the Mongol Derby on August 10, 2013; she ultimately won the race, finishing in seven days. Photograph by Richard Dunwoody, The Adventurists

Why a Horse Race?

Though the competitors have varying levels of experience, one key element brings most of them together: their interest in learning about riding from those who have been said to do it best—Mongol herders.

"High Asia is where horses were first saddled and tamed and ridden, so it's one of the oldest equestrian cultures, and they really admire and respect the horse in a kind of spiritual way," Willings explains.

Every ger, the herders' portable yurt-like homes, has ropes made from the tail hairs of its owner's favorite horses, and the countryside is littered with rock cairns called ovoos where herders have placed tails or skulls of particularly beloved horses.

Willings says that Mongolians-despite their deep affection for their horses—view them differently than Westerners view the animals. "They are not pets. They're not for school. They're not for leisure," she says. "They're working animals, and part of the family, and a great symbol of a family's wealth."

As such, the horse is deeply ingrained in Mongolian culture. There is a special song for the horses that finish last in the race during the annual Naadam festival so that they do not feel sad about losing.

Herders write songs for their horses and serenade them as they watch over them or when they are milking their mares. The national drink of Mongolia is fermented mare's milk, also known as airag. Besides riding for the title of the 2014 winner of the Mongol Derby, the winner also gets the honor of drinking the first bowl of airag.

View Images Craig Egberink of South Africa walks a horse into a station during the 2011 Derby. A rider is penalized if he or she pushes a horse too hard and its heart rate is too fast at the end of a 25-mile leg. Photograph by Charles van Wyk, The Adventurists

The Horses

Willings says Mongolian horses are unique for several reasons. Genetically, they are considered to be horses despite being the size of a pony. A horse is typically 5 feet (157 centimeters) or taller at the base of the neck. While on average Mongol horses are only 4.6 feet (143 centimeters) tall, they are considered horses because of their head structure and bone size.

Despite their diminutive size, today's Mongol horses are the same breed ridden by Genghis Khan's conquering warriors—able to run long distances, even from Mongolia to Poland and back, and to withstand a wide range of temperatures, from -40 to 90 degrees Fahrenheit (-40 to 30 degrees Celsius).

Despite their diminutive size, today's Mongol horses are the same breed ridden by Genghis Khan's conquering warriors.

They also can handle rugged terrain. The Mongolian steppe is peppered with marmot holes, something all previous Mongol Derby riders learned to dread early in the races. With any other horse, the marmot holes would spell serious danger because the holes are waist deep. "But because these horses live in this environment year-round, they just know," says Willings. "They read the ground so cleverly. They are geniuses in their natural environment."