The circle above indicates the time we discuss in this section
Introduction of the Five Main Sword Schools (Den)
There are five major sword schools (den): Yamashiro-den (山城), Bizen-den (備前), Soshu-den (相州), Yamato-den (大和), and Mino-den (美濃). During the Heian period, Yamashiro-den was the main and most active school. A school called Ko-bizen (meaning old Bizen) during the Heian period is part of the Bizen-den. However, we consider Ko-bizen separately because its style is slightly different from the later Bizen-den, yet somewhat similar to Yamashiro-den as we see it later.
During the Heian period, the swordsmiths of Yamashiro-den lived around Kyoto, which was Japan’s capital at the time. In the early Kamakura period, Yamashiro-den maintained a sword style similar to the one they had created during the Heian period. Bizen-den emerged in the middle Kamakura period. Soshu-den appeared in the late Kamakura period in the Kamakura area. Mino-den appeared later during the Muromachi period, which came much later.
The Early Kamakura Period (鎌倉)
We divide the Kamakura period into three stages: the Early, Middle, and Late Kamakura periods. The sword style during the early Kamakura period was almost the same as in the previous Heian period. Yamashiro-den remained the most active school throughout the early Kamakura period.
The Middle Kamakura Period (1219-1277)
During the middle Kamakura period, there were three main sword styles to discuss: the Yamashiro-den style, the Bizen-den style, and the Ikubi-kissaki (猪首切先) style, which was a new development at the time. We can say that among Ikubi-kissaki swords, it is rare to find a mediocre one.
The previous section explained how the Kamakura Bakufu (鎌倉幕府: government) held political and military power, but the emperor remained on the throne in Kyoto. Emperor Gotoba raised an army and attacked the Kamakura government to regain political control. This war (1221) is known as Jyokyu-no-ran (承久の乱). The war caused the shape of swords to change to a sturdier look. This style is what we now call the Ikubi-kissaki.
The Late Kamakura Period (1278-1333 after the Mongolian Invasion)
During the late Kamakura Period, the Soshu-den emerged alongside Yamashiro-den and Bizen-den. After the two Mongolian invasions known as the Genko (元寇) in 1274 and 1281, swords with longer, wider blades and longer kissaki began to appear. The Soshu-den swordsmiths forged this type of sword
Engravings on Sword
Engravings on swords from the Ko-to era (Heian to Keicho era) serve three purposes. One is to reduce the weight of the sword, such as hi, bohi, and gomabashi (wide, narrow, short, or long grooves), for example. The second is for religious reasons, as swordsmiths often carved Buddhist figures. The third is for decoration. In the shin-to era (from Keicho time onward), it became mainly for decorative purposes.
The figures below show examples of the engravings.
Suken Bonji (Sanskrit) Gomabashi Hi
Study of Japanese Sword 