and provincial governor Zhang Yichao riding triumphantly after the recapture and conquest of the Dunhuang region from the Tibetan Empire in 834 AD. According to evidence provided by Dr. Chang Shuhong, the date of the painting is precisely 851 AD, yet Needham points out that there is universal consensus amongst historians that it was painted anytime between roughly 840 to 860 AD. This latter painting accurately depicts the horse collar, with a well-padded collar coming low on the chest and rising behind the cross-bar. Europe The horse collar eventually spread to Europe c. 920 AD, and became universal by the 12th century. The Scandinavians were among the first to use a horse collar that did not constrain the breathing passages of the horses. Prior to this development, oxen still remained the primary choice of animal for farm labor, as all the previous harnesses and collars could only be worn by them without physical penalty. Additionally, the yoke used to harness oxen were made exclusive to each individual animal. However it was sometimes difficult to cultivate the land; based upon soil condition, it may have taken up to sixteen oxen to effectively use a single heavy plow. This made it difficult for farmers who lacked the capital to sustain such large numbers. When the horse was harnessed with a horse collar, the horse could apply 50% more power to a task than an ox due to its greater speed. Horses generally also have greater endurance and can work more hours in a day. The centuries-long association that the Europeans had with the use of horses allowed an easier transition from oxen-based harnesses to the horse collar. Impact of the horse collar The creation of the horse collar removed the previous physical restrictions the old harness had on the animal, and allowed the horse to be able to exert its full strength in plowing. Originally, the structure of the old harness forced the horse to literally pull its workload, the horse collar's development instead allowed the horse to push its workload, increasing the efficiency of its labor output. Following the introduction of the horse collar to Europe and its use being clearly evident by 1000 AD, the use of horses for ploughing became more widespread. Horses work roughly 50 percent faster than oxen. With the collar, combined with the horseshoe, the heavy plow, and other developments in the agricultural system, the efficiency