Most inventions are remarkable because they appear to be ahead of their time, revelatory events that transform the world into which they appear. The horse collar seems to be somewhat the opposite, for it is difficult to see why it was not invented earlier.
The problem to be solved is obvious: A horse wearing a simple harness can pull a load weighing about 135 pounds (60 kg), but any heavier load forces the harness on to the horse's windpipe, and restricts its ability to breathe. Therefore, while horses had been domesticated, mounted, saddled, and harnessed by around 100—and so could be ridden for pleasure, work, or warfare—their role as a beast of burden was necessarily limited, and was to remain so for another 400 years.
It was not until circa 500 that a Chinese camel driver had the bright idea of devising a padded collar, which was quickly used also on horses. It took the form of a rigid construction that sat low on the horse's chest and rose round its neck to rest on its withers or shoulders. The top of the collar supported a pair of curved metal or wood hames, to which the harness was attached. The collar reduced pressure on the windpipe and allowed the horse to use its full strength, thus allowing it to push forward with its hindquarters into the collar rather than pull the weight with its shoulders.
This new design of collar reached Europe circa 920, and soon revolutionized agriculture. Horses replaced oxen as the main beasts of burden, pulling plows, harrows, harvesting machines, and other agricultural implements, as well as farm carts and wagons.
