Legend maintains that natto was first discovered by soldiers on campaign in northeastern Japan about 1000 years ago. Rather than leave a pot of cooked soybeans behind when they needed to break camp on short notice, the beans were packed into straw baskets. When the bags were opened a few days later, the beans had been transformed into natto.
More likely, natto and other fermented soybean products originated somewhere in the Yunnan province of China. Given that all the required tools and ingredients are naturally occurring across Asia, it is possible that natto or something similar was being produced as far back as the Bronze Age, 4000 years ago.
The first recorded instance of the word “natto” is from 1068, in the Shin Sarugaku Shiyu, a novel by a Heian-period noblewoman named Fujiwara Akihira, which recorded many details of daily life at the time. Natto was likely already well known by this time; the ancient word “kuki” was used to describe a variety of fermented soy products, including some that would be recognized as natto.
Natto production, especially of salted natto, was especially associated with temples. In fact, the word “natto” roughly translates as “temple beans”. According to local legend in Kyoto, the Emperor Kogan retired from his brief reign to become a monk, and helped to popularize natto as a temple food. Natto came to be an important source of protein and nutrients in a monk’s vegetarian diet, and was also given as a religious offering. Military leaders also prized natto as a hearty food with a reputation for boosting stamina. During the Tokugawa Shogunate, monks gave annual gifts of natto to the shogun, who in turn used it to provision his soldiers. In more recent times, temples distributed natto to their parishioners at New Years celebrations.