How long has shoyu (soy sauce) been used in Japan?

The first known descriptions of shoyu, or soy sauce, appeared in literature during the middle of the Muromachi period (1333－1568) and at the end of the 16th century when soy sauce became common among ordinary people.
However, the original form of soy sauce dates back to the pre-Nara period (710-794), when hishio, fermented sauce containing grain, meat, fish, vegetables, seaweed and so forth was used.
Soy sauce as well as soybean paste (miso) developed from this sauce.
Different kinds of soy sauce used presently, such as tamari (thick sauce), koikuchi (dark sauce) and usukuchi (light sauce), were made during the Edo period (1600-1868).