A horse race is a competition in which horses are driven by jockeys to the finish line on a designated course, usually around an oval or rectangular track. If the horse crosses the finish line first, it receives a certain amount of prize money. If no one finishes first, the winner is determined by a photo finish. The first documented horse race was held in 1651 in France as the result of a wager between two noblemen. By the time of Louis XIV (reigned 1643-1715), horse racing was firmly established as an industry that depended on betting, with rules and regulations created based on age, sex, birthplace and previous performance to determine eligibility for races. By the mid-18th century, demands for more public races led to a wide variety of events and rulebooks. For instance, a race may be a stakes race in which the owner must pay a fee for nominating, maintaining eligibility, entering and starting; to which the track adds a set amount of prize money to make up the total purse. Alternatively, a race may be considered an open event in which the owner pays no fees but must meet minimum requirements to compete. While many races still adhere to a traditional format, technological advances have made horse racing more scientific than ever before. For example, thermal imaging cameras help monitor the safety and health of a horse after a race; MRI scanners, X-rays and endoscopes allow veterinarians to diagnose and treat minor or major injuries; and 3D printing can produce casts and splints for injured or ill horses. A thoroughbred is a breed of race horse that is characterized by its size, speed and endurance. The word “stretch” is often used to describe the length of stride of a thoroughbred. In general, a thoroughbred with longer strides will be faster than a shorter-striding horse. When a horse loses its balance or staggers during a race, it is said to have fallen. A fall can be caused by an unbalanced rider, a slippery surface, bad weather, a misstep or even a faulty stirrup. A horse that falls can also be disqualified if it interferes with another competitor. A horse that wins a large number of races over a short period of time is considered a champion. Traditionally, champions have been male and female horses that have won three of the American Triple Crown races—the Belmont Stakes (1867), Preakness Stakes (1873) and Kentucky Derby (1975). Only 13 horses have achieved this prestigious feat in the United States. Other countries have their own series of classic races, but these do not include the Triple Crown.