With allowance for the possibility that not all the horses may have been intended for simultaneous use, the more than sixty Shang and a hundred Chou sites containing chariots and horses already excavated in north and central China (among thousands of graves and tombs) sustain the conclusion that Shang chariots invariably employed just a single pair.39 In almost every case the remnant chariots had two horses harnessed or placed alongside them irrespective of the grave’s opulence, and Shang oracular inscriptions sometimes refer to pairs of horses.40 Moreover, initial reports of a chariot accompanied by four horses at M20 at Anyang have now been retracted, and no other site that can definitively be dated to the Shang has yet provided any evidence to the contrary.41 Even the most extensive Chou dynasty tombs rarely include four-horse teams, despite their initial employment at the Chou’s inception and escalating employment on Spring and Autumn battlefields.
However, the proto-state of Chou, which may have been the transmission nexus for the chariot and therefore somewhat further along the experiential curve, seems to have initiated the practice of using four-horse teams in warfare, exploiting them to decisive advantage at the Battle of Mu-yeh for the first time.42 The Shih Ching, hardly the most reliable guide to actual practice, always refers to four horses being employed in Western Chou military campaigns, a number confirmed by several interments. Thereafter, whether uncovered in tombs with single or multiple chariots, the ratio varies among two, four, or six horses to one chariot, though four-horse versions would increasingly dominate as chariot-centered warfare proliferated in the Spring and Autumn and became almost universal in the Warring States, just when their importance was diminishing because of the growth of mass infantry contingents. 43 Nevertheless, two- and four-horse chariots are still found in late Warring States sites, and several different basic types and sizes, intended for different purposes, coexisted across the years.
Apart from the complexities of harnessing and control, adding an additional pair of horses complicated management and logistical efforts considerably. The cost of outfitting the chariot soared, training requirements increased, equine behavioral and health problems multiplied, and vulnerability soared with the increased number of horses that might be wounded or suffer injury.
The advantage conveyed by additional horses depends on a number of factors, especially the efficiency of the harness, weight of the chariot, and difficulty of the terrain. If a pair of horses can attain the maximum speed theoretically achievable on a particular terrain, more horses merely diminish the work effort required from each, possibly at too great an overall cost if sustained racing is not tactically required. On rough terrain where increased traction power was necessary or distant battlefields where speed could prove crucial, a four-horse team would allow longer employment under stress and provide a decided advantage. Four horses were also far more prestigious and formidable, clearly favored by anyone bent on ostentatious display or creating awesomeness.
No doubt to curb human proclivity for conspicuous display, sumptuary rules gradually came into effect during the Western Chou that attempted to constrain the types of chariots, carriages, and ornamentation that might be employed, whether in ordinary life or burial. Warring States writers with a propensity for systematization and idealization believed that the number should be a function of rank, with only the emperor being accorded the privilege of driving a team of six horses. Feudal lords would then be allowed four and higher officers two, with most transport carriages being confined to two horses but generally protected by an umbrella. Nevertheless, a few feudal lords usurped imperial prerogative by employing six horses, while many rich and powerful individuals reportedly flaunted their status with four.44
The traditionally held belief that the sumptuary regulations exerted a pervasive influence in the Warring States period, their period of systematic formulation, has recently come into increasing question, particularly with respect to whether the Chou king ever drove a team of six.45 Apart from questions about how they might have been hitched (because only a single shaft was employed until the end of the Warring States period) and their no doubt limited effectiveness (presumably consigning them largely to display), Chou era burials containing six horses matched with a single chariot are isolated and extremely rare. Nevertheless, they do exist, suggesting that they were in fact employed in rare cases, including for the battlefield.46 There are also Warring States textual references to using six horses, including in the Yen-tzu Ch’un-ch’iu, which indicates that the sagacious Yen-tzu found this practice presumptive and therefore offensive.