The Thoroughbred is a horse breed best known for its use in horse racing. The Thoroughbred is a distinct breed of horse, though people sometimes refer to a purebred horse of any breed as a "thoroughbred". The typical Thoroughbred ranges between 15.2 to 17.0 hands (hh) high (62 to 68 inches (157 to 173 cm)), averaging 16 hh (64 inches (163 cm)). Flat racing existed in England by at least 1174, when four mile races took place at Smithfield, in London. All modern Thoroughbreds trace back to three stallions imported into England from the Middle East in the late 17th and early 18th centuries: the Byerley Turk (1680), the Darley Arabian (1704), and the Goldophin Arabian (1729). The mares used as foundation breeding stock came from a variety of breeds, some of which, such as the Irish Hobby, had developed in northern Europe prior to the 13th century. By the end of the 18th century, the English Clasic races had been established. The first Thoroughbred horse in the American collonies was Bulle Rock, imported in 1730 by Samuel Gist of Hanover County, Virginia. Thoroughbreds began to be imported to France in 1817 and 1818 with the importation of a number of stallions from England, but initially the sport of horse racing did not prosper in France. Horses arrived in Australia with the First Fleet in 1788 along with the earliest colonists. Thoroughbreds have been exported to many other areas of the world since the breed was created. About 37,000 Thoroughbred foals are registered each year in North America, with the largest numbers being registered in the states of Kentucky, Florida and California. Prices on Thoroughbreds vary greatly, depending on age, pedigree, conformation, and other market factors. Although the Thoroughbred is primarily bred for racing, this breed is also used for show jumping and combined training because of its athleticism, and many retired and retrained race horses become fine family riding horses, dressage horses, and youth show horses. Thoroughbred horses are primarily bred for racing under at the gallop. In addition to racing, Thoroughbreds compete in eventing, show jumping, and dressage at the highest levels of international competition, including the Olympics. Thoroughbreds are often crossed with horses of other breeds to create new breeds or improve existing ones. Although Thoroughbreds are seen in the hunter-jumper world and in other disciplines, modern Thoroughbreds are primarily bred for speed, and racehorses have a very high rate of accidents as well as other health problems. One argument for the health issues involving Thoroughbreds suggests that inbreeding is the culprit. A high accident rate may also occur because Thoroughbreds, particularly in the United States, are first raced as 2-year-olds, well before they are completely mature. But also controversial, due in part to the significant challenges in treating broken bones and other major leg injuries.