The two words "yao" and "bi", which were also written as "mao（瞀 or 冒）" and " bi（辟）", are often used together in the lists of military equipment recorded in Han dynasty wooden and bamboo slips found at northwest garrison sites, forming language structures like "pi-yao-cao-bi", "pi-mao-cao-bi", "yang-pi-mao-bi" or "cao-pi-ji-mao". The word "pi-yao" has been researched by many scholars but its meaning remains unknown and no research has been done on the word "bi". Some scholars think that they seem to be equivalent to "zhou and jia (helmet and armor)" as they are often used together. A general examination of all the examples found in these slips suggests that "zhou and jia" are fixed words or expressions. According to our researches, "yao" and "bi" were equipments necessary for the scouts on watch, the former used for keeping watch, the latter for defending and shelter.
