horses in harness, particularly for ploughing and other farm work, was the horse collar. The horse collar was invented in China during the 5th century, arrived in Europe during the 9th century, and became widespread throughout Europe by the 12th century. It allowed horses to pull greater weight than they could when hitched to a vehicle by means of yokes or breastcollars used in earlier times. The yoke was designed for oxen and not suited to the anatomy of horses, it required horses to pull with their shoulders rather than using the power of their hindquarters. Harnessed in such a manner, horse teams could pull no more than 500 kg. The breastplate-style harness that had flat straps across the neck and chest of the animal, while useful for pulling light vehicles, was of little use for heavy work. These straps pressed against the horse's sterno-cephalicus muscle and trachea, which restricted breathing and reduced the pulling power of the horse. Two horses harnessed with a breastcollar harness were limited to pulling a combined total of about . In contrast, the horse collar rested on horses' shoulders and did not impede breathing. It allowed a horse to use its full strength, by pushing forward with its hindquarters into the collar rather than to pull with its shoulders. With the horse collar, a horse could provide a work effort of 50% more foot-pounds per second than an ox, because it could move at a greater speed, as well as having generally greater endurance and the ability to work more hours in a day. A single horse with a more efficient collar harness could draw a weight of about . A further improvement was managed by altering the arrangement of the teams; by hitching horses one behind the other, rather than side by side, weight could be distributed more evenly, and pulling power increased. This increase in horse power is demonstrated in the building accounts of Troyes, which show carters hauling stone from quarries distant; the carts weighed, on average, , on which of stone was regularly loaded, sometimes increasing to – a significant increase from Roman-era loads. Horse trades and professions The elite horseman of the Middle Ages was the knight. Generally raised from the middle and upper classes, the knight was trained from childhood in the arts of war and management of the horse. In most languages, the term for knight reflects