Horses in warfare
Types of horse used in warfare: A fundamental principle of equine conformation is "form to function". Therefore, the type of horse used for various forms of warfare depended on the work performed, the weight a horse needed to carry or pull, and distance travelled. Weight affects speed and endurance, creating a trade-off: armour added protection, but added weight reduced maximum speed. Therefore, various cultures had different military needs. In some situations, one primary type of horse was favoured over all others. In other places, multiple types were needed; warriors would travel to battle riding a lighter horse of greater speed and endurance, and then switch to a heavier horse, with greater weight-carrying capacity, when wearing heavy armour in actual combat.
The average horse can carry up to approximately 30% of its body weight. While all horses can pull more weight than they can carry, the maximum weight that horses can pull varies widely, depending on the build of the horse, the type of vehicle, road conditions, and other factors. Horses harnessed to a wheeled vehicle on a paved road can pull as much as eight times their weight, but far less if pulling wheelless loads over unpaved terrain. Thus, horses that were driven varied in size and had to make a trade-off between speed and weight, just as did riding animals. Light horses could pull a small war chariot at speed. Heavy supply wagons, artillery, and support vehicles were pulled by heavier horses or a larger number of horses. The method by which a horse was hitched to a vehicle also mattered: horses could pull greater weight with a horse collar than they could with a breast collar, and even less with an ox yoke.

Light-weight: Light, oriental horses such as the ancestors of the modern Arabian, Barb, and Akhal-Teke were used for warfare that required speed, endurance, and agility. Such horses ranged from about 12 hands (48 inches, 122 cm) to just under 15 hands (60 inches, 152 cm), weighing approximately 360 to 450 kilograms (800 to 1,000 lb). To move quickly, riders had to use lightweight tack and carry relatively light weapons such as bows, light spears, javelins, or later rifles. This was the original horse used for early chariot warfare, raiding, and light cavalry.
Relatively light horses were used by many cultures, including the Ancient Egyptians, the Mongols, the Arabs, and the Native Americans. Throughout the Ancient Near East, small, light animals were used to pull chariots designed to carry no more than two passengers, a driver and a warrior. In the European Middle Ages, a lightweight war horse became known as the rouncey.

Medium-weight: Medium-weight horses developed as early as the Iron Age with the needs of various civilizations to pull heavier loads, such as chariots capable of holding more than two people, and, as light cavalry evolved into heavy cavalry, to carry heavily armoured riders. The Scythians were among the earliest cultures to produce taller, heavier horses. Larger horses were also needed to pull supply wagons and, later on, artillery pieces. In Europe, horses were also used to a limited extent to maneuver cannons on the battlefield as part of dedicated horse artillery units. Medium-weight horses had the greatest range in size, from about 14.2 hands (58 inches, 147 cm) but stocky, to as much as 16 hands (64 inches, 163 cm), weighing approximately 450 to 540 kilograms (1,000 to 1,200 lb). They generally were quite agile in combat, though they did not have the raw speed or endurance of a lighter horse. By the Middle Ages, larger horses in this class were sometimes called destriers. They may have resembled modern Baroque or heavy warmblood breeds. Later, horses similar to the modern warmblood often carried European cavalry.

Heavy-weight: Large, heavy horses, weighing from 680 to 910 kilograms (1,500 to 2,000 lb), the ancestors of today's draught horses, were used, particularly in Europe, from the Middle Ages onward. They pulled heavy loads like supply wagons and were disposed to remain calm in battle. Some historians believe they may have carried the heaviest-armoured knights of the Late Medieval Period, though others dispute this claim, indicating that the destrier, or knight's battle horse, was a medium-weight animal. It is also disputed whether the destrier class included draught animals or not. Breeds at the smaller end of the heavyweight category may have included the ancestors of the Percheron, agile for their size and physically able to maneuver in battle.

Ponies: The British Army's 2nd Dragoons in 1813 had 340 ponies of 14.2 hands (58 inches, 147 cm) and 55 ponies of 14 hands (56 inches, 142 cm); the Lovat Scouts, formed in 1899, were mounted on Highland ponies; the British Army recruited 200 Dales ponies in World War II for use as pack and artillery animals; and the British Territorial Army experimented with the use of Dartmoor ponies as pack animals in 1935, finding them to be better than mules for the job.

Other equids: Horses were not the only equids used to support human warfare. Donkeys have been used as pack animals from antiquity to the present. Mules were also commonly used, especially as pack animals and to pull wagons, but also occasionally for riding. Because mules are often both calmer and hardier than horses, they were particularly useful for strenuous support tasks, such as hauling supplies over difficult terrain. However, under gunfire, they were less cooperative than horses, so were generally not used to haul artillery on battlefields. The size of a mule and work to which it was put depended largely on the breeding of the mare that produced the mule. Mules could be lightweight, medium weight, or even, when produced from draught horse mares, of moderate heavy weight.

Training and deployment: The oldest known manual on training horses for chariot warfare was written c. 1350 BC by the Hittite horsemaster, Kikkuli. An ancient manual on the subject of training riding horses, particularly for the Ancient Greek cavalry is Hippike (On Horsemanship) written about 360 BC by the Greek cavalry officer Xenophon. and another early text was that of Kautilya, written about 323 BC.
Whether horses were trained to pull chariots, to be ridden as light or heavy cavalry, or to carry the armoured knight, much training was required to overcome the horse's natural instinct to flee from noise, the smell of blood, and the confusion of combat. They also learned to accept any sudden or unusual movements of humans while using a weapon or avoiding one. Horses used in close combat may have been taught, or at least permitted, to kick, strike, and even bite, thus becoming weapons themselves for the warriors they carried.
In most cultures, a war horse used as a riding animal was trained to be controlled with limited use of reins, responding primarily to the rider's legs and weight. The horse became accustomed to any necessary tack and protective armour placed upon it, and learned to balance under a rider who would also be laden with weapons and armour. Developing the balance and agility of the horse was crucial. The origins of the discipline of dressage came from the need to train horses to be both obedient and manoeuvrable. The Haute ecole or "High School" movements of classical dressage taught today at the Spanish Riding School have their roots in manoeuvres designed for the battlefield. However, the airs above the ground were unlikely to have been used in actual combat, as most would have exposed the unprotected underbelly of the horse to the weapons of foot soldiers.
Horses used for chariot warfare were not only trained for combat conditions, but because many chariots were pulled by a team of two to four horses, they also had to learn to work together with other animals in close quarters under chaotic conditions.

Technological innovations: Horses were probably ridden in prehistory before they were driven. However, evidence is scant, mostly simple images of human figures on horse-like animals drawn on rock or clay. The earliest tools used to control horses were bridles of various sorts, which were invented nearly as soon as the horse was domesticated. Evidence of bit wear appears on the teeth of horses excavated at the archaeology sites of the Botai culture in northern Kazakhstan, dated 3500–3000 BC.

Harness and vehicles: The invention of the wheel was a major technological innovation that gave rise to chariot warfare. At first, equines, both horses and onagers, were hitched to wheeled carts by means of a yoke around their necks in a manner similar to that of oxen. However, such a design is incompatible with equine anatomy, limiting both the strength and mobility of the animal. By the time of the Hyksos invasions of Egypt, c. 1600 BC, horses were pulling chariots with an improved harness design that made use of a breastcollar and breeching, which allowed a horse to move faster and pull more weight.
Even after the chariot had become obsolete as a tool of war, there still was a need for technological innovations in pulling technologies; horses were needed to pull heavy loads of supplies and weapons.