The harness is the working gear of a draft animal, made chiefly of leather. When pairs of oxen were first used for plowing (about 4000 B.C.), their yokes were pegged to a center pole and held in place by neck straps; control was achieved through reins attached to each animal's lip ring. The breast harness was added in the next millennium, when slender-shouldered onagers, often four in a row, were yoked to light vehicles.
By about 1550 B.C. the bridle and bit had been introduced in the Middle East and Europe for horses that drew war chariots. In classical times the tandem harness was devised, and single animals were placed in traces (usually straps that joined the harness to the vehicle) or occasionally in shafts. But the ancient world never learned how to prevent the horse harness from constricting the animal's windpipe and jugular vein.
The development of the collar harness increased the horse's effective pulling power about fourfold and made it possible to replace oxen with horses where the latter's greater power and speed were important. Such harnesses were in use in China by 500 A.D., and they became widely used in Europe during the 9th to 12th centuries. In northern Europe, where the soil must be cultivated rapidly because of the short growing season, the collar harness made it possible for the horse to replace the ox in the plow, and throughout much of Europe horses largely replaced oxen for hauling carts and wagons.
The key part of the collar harness is a stiff padded collar with rigid projections (names) to which the traces or shafts are attached. The advantage of the harness is that the horse can push against the collar full force without impeding its breathing or circulation.