The Thoroughbred is a horse breed best known as a race horse. While carefully bred racehorses had existed throughout Europe for centuries prior to this time, the breed as it is known today developed during the 17th century in England when English mares began to be bred to imported Arabian stallions. This addition of verifiable Arabian blood coincided with the creation of the General Stud Book of England and the practice of official registering of horses. Today all modern Thoroughbreds trace to these imported stallions. For more information about the Tennessee Walking Horse breed please see our Tennessee Walker Breed page.