There are a number of theories regarding the domestication of the horse. Although horses appeared in Paleolithic cave art as early as ca 30,000 BC, these were truly wild horses and were probably hunted for meat; how and when horses became domesticated is less clear. The most common date of domestication and use as a means of transport is c. 2000 BC, although in the Kurgan hypothesis the domestication of horses is dated as early as 4500 BC.
Incontrovertible evidence of domestication comes from archaeological finds of human artifacts connected with horses:
- depictions of horses used as mounts or draught animals
- equipment such as bits or other types of horse tack
- horse remains in archaeological context, particularly horses interred in human graves or showing other signs of ceremonial burial.
Studies of morphological features of existing animals compared to those of fossil remains (frozen remains, other preserved remains, and sub-fossils) led to the hypothesis that horses were domesticated in one small area of the great steppes of Eurasia, perhaps around the mid 5th millennium. The earliest archaeological evidence of domestication are bone bits and horse remains in human graves found in the eneolithic (5th millennium) Samara culture at the middle Volga. Interestingly, this same culture is suggested to correspond to the Proto-Indo-Europeans in the Kurgan hypothesis.
It remains for archaeology to find and excavate the sites that will tell us what happened. In historical times, the use of horses is nearly a diagnostic of Indo-European culture in the diaspora phase. It is certainly one if hardly the only way to account for the rapid spread of the Kurgan culture and the ease with which it seems to have gotten the upper hand over Pre-Indo-European cultures. For the most part, the forest-steppe region and the plains of Asia remain archaeologically unexplored, leaving room for future discoveries.
The earliest incontrovertible evidence of horses used as trained animals are the chariot burials of the Sintashta-Petrovka culture, dating to around 2000 BC.
The earliest evidence of horse domestication spreading outside regions that encompassed the wild horse's natural habitat is found in early depictions of horses as draught animals in the Ancient Near East, dating to ca. 1800 BC. These images showed harnessed horses controlled with nose rings, as was also the practice with the onagers (Equus hemionus) native to the Near East; horses controlled in such a manner could draw chariots in processions, but not in battle. Widespread introduction of the horse to the Near East coincides with the turmoil of the Kassite period from ca. 1600 BC.
The first evidence of domesticated horses in China dates to the late Bronze Age Yin Dynasty, and evidence for introduction to the Indian Subcontinent (see History of the horse in South Asia) and Northern Europe (see Trundholm sun chariot) date to about the same period.
While riding may have been practiced during the 4th and 3rd millennia BC, the first known impact by horses on ancient warfare was by pulling chariots, introduced circa 2000 BC.
Horses in the Bronze Age were relatively small by modern standards, which led some theorists to believe the ancient horses were too small to be ridden and so must have been driven. Herodotus' description of the Sigynnae, a steppe people who bred horses too small to ride but extremely efficient at drawing chariots, illustrates this stage.
The Iron Age saw the rise of mounted cavalry as a tool of war, as evidenced by the notable successes of mounted archer tactics used by various invading equestrian nomads such as the Parthians. Over time, the chariot gradually become obsolete.
The horse of the Iron Age was still relatively small, perhaps 12.2 to 14.2 hands high or 1.27 to 1.47 meters, measured at the withers. This was shorter overall average height than modern riding horses, which range from 14.2 to 17.2 hh (1.47 to 1.8 meters). However, small horses were used successfully as light cavalry for many centuries. For example, Fell ponies, believed to be descended from Roman cavalry horses, are comfortably able to carry fully grown adults (although with rather limited ground clearance) at an average height of 13.2 hands (1.37 m). Likewise, the Arabian horse is noted for a short back and dense bone, and the successes of the Muslims against the heavy mounted knights of Europe demonstrated that a 14.2 hand horse can easily carry a full-grown human adult into battle.
Mounted warriors such as the Scythians, Huns and Vandals of late Roman antiquity, the Mongols who invaded eastern Europe in the 7th century through 14th centuries AD, the Muslim warriors of the 8th through 14th centuries AD, and the American Indians in the 16th through 19th centuries each demonstrated effective forms of light cavalry.