The horse (Equus ferus caballus) is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved (ungulate) mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today. Humans began to domesticate horses around 4000 BC, and their domestication is believed to have been widespread by 3000 BC. Horses in the subspecies caballus are domesticated, although some domesticated populations live in the wild as feral horses.
Horse racing is an equestrian sport that has a long history. Archaeological records indicate that horse racing occurred in ancient Babylon, Syria, and Egypt. Both chariot and mounted horse racing were events in the ancient Greek Olympics by 648 BC. In the Roman Empire, chariot and mounted horse racing were major industries. Thoroughbred racing was popular with the aristocrats and royalty of British society, earning it the title "Sport of Kings."