Mounted horseracing has been around ever since humans learned to ride the animals. During the Crusades, many English knights brought back from their travels fast Arabian horses, which they bred with English horses to produce a line of strong and swift runners. The nobility often paired these horses in head-to-head races to determine which was the fastest — with, of course, a friendly wager as to the outcome — and the “sport of kings” was born.

For the last two centuries, Thoroughbreds have been bred for their speed, agility, and stamina. The breed's long legs allow it to cover more ground with every stride, while its wide girth gives it greater lung capacity. Sloping shoulders and powerful hindquarters also contribute to the Thoroughbred's outstanding running speed.

These common characteristics notwithstanding, Thoroughbreds develop individual running styles through the course of their training and racing careers.

Some, called “frontrunners,” “pacesetters,” or “speedsters,” like to lead the field from a race's beginning to the finish line. Others, called “stalkers,” would rather hang back from the early leaders and slowly advance during the race.

Some, called “closers,” “late runners,” or “stretch runners,” prefer to conserve their energy until the final stages of the races, when they typically come on with furious speed from the back of the field.

To be classified as a Thoroughbred, a horse's lineage must be traceable to sires listed in the General Stud Book. In fact, the breeding has been so selective that every one of today's registered Thoroughbreds can trace its pedigree back to one of three foundation sires: Byerley Turk (1679), Darley Arabian (1700), or Godolphin Arabian (1724).