The horse (Equus caballus or Equus ferus caballus) is a sizeable ungulate mammal, one of ten modern species of the genus Equus. Horses have long been one of the most economically important domesticated animals, and have played an important role in the transport of people and cargo for thousands of years. Most notably, horses can be ridden by a person perched on a saddle attached to the animal, and are also widely harnessed to pull objects like wheeled vehicles or plows. In some human cultures, horses are also widely used as a source of food. Though isolated domestication may have occurred as early as 4500 BC, clear evidence of widespread use by humans dates to no earlier than 2000 BC, as evidenced by the Sintashta chariot burials, thus firmly establishing the domestication of the horse.