In ancient times, the power of horse-drawn carriages was limited. As it was, the animal was attached to the vehicle by a soft leather strap around its neck. It was necessary to limit the weight of loads, since the horse might choke from the pressure of the strap on the trachea.
A major technological innovation, the shoulder collar led to a significant improvement in draft horse performance.
Developed over the centuries throughout Rome, the gradual lowering of the pull point below the throat of the animal led to the use of the shoulder collar, which spread in the Middle Ages. The stiff shoulder collar avoided compression on the trachea while maintaining the animal's pulling power. The shoulder collar therefore led to a significant improvement in performance by shifting the weight of the load to the animal's shoulders. It thus enabled using the horse for tasks that were previously reserved for oxen.