The American Quarter Horse, or Quarter Horse, is an American breed of horse that excels at sprinting short distances. Its name is derived from its ability to outrun other horse breeds in races of a quarter mile or less; some have been clocked at speeds up to 55 mph (88.5 km/h). The Quarter Horse breed began when colonists in the 1600s on the Eastern seaboard of what today is the United States began to breed imported English Thoroughbred horses with assorted “native” horses. This included the Chickasaw horse, which was a breed developed by Native American people from horses descended from Spain and brought to the United States by the Conquistadors. These horses were developed from Iberian, Arabian and Barb stock brought to what is now the Southeastern United States.