The samurai sword underwent changes throughout the Kamakura Period (1185-1333). Before the Kamakura shogunate was founded, civil power in Japan mostly belonged to emperors and their regents. But after overthrowing the Taira clan in the Genpei War, Minamoto no Yoritomo of the rival Minamoto clan usurped certain powers from the aristocracy and established the Kamakura shogunate in Kamakura.
While Emperor Gotoba in Kyoto remained the formal ruler, the Kamakura shogunate was officially recognized in 1192 and Minamoto no Yoritomo became the first shogun. After his death, his wife’s family, the Hojo clan, took control and maintained power from 1203-1333 under the title of shikken (regent to the shogun). The era came to an end in 1333 when the shogunate was destroyed.
The Kamakura period is known for the beginning of the rule of the samurai warrior class, and for producing the best handmade samurai swords in Japanese history. Masamune, Japan’s greatest swordsmith, was active during the late Kamakura period.
Early Kamakura (1185-1231) Swords
During this time, the Kamakura shogunate fought for political authority against the aristocracy in Kyoto, as well as struggled with its own internal problems. As a result, demand for swords grew. The samurai sword of this era differed from its predecessor of the Heian period.
The shape of the blade changed from refined to strong. The sori (curvature) moved up from right above the nakago (tang). The term for this type of sori is koshi-zori, where the deepest part of a blade’s curve is at its waist. The width of the monouchi (the first six inches from the kissaki (point)) and the area near the nakago were similar. The kissaki slightly increased in size, the temper line was straight (suguha), and the crystals in the temper line and blade surface were small (ko-nie). The average blade length was 79 cm.
Middle Kamakura (1231-1287) Swords
Swordsmiths from other parts of Japan moved to Kamakura at the request of the shogunate, turning the city into the heart of samurai culture and the center of sword making. Meanwhile, the steady demand for samurai katana swords continued.
Blades of this period became wider and thicker. Other features were ikubi (literally “boar’s neck”, a short and wide kissaki); hamaguri-ba (clam-shaped edge); a slightly longer nakago; and a more obvious hamon (temper pattern). Some popular hamon styles during this period were the obusa-choji and juka-choji, invented by the Fukuoka-Ichimonji School in Bizen. Choji means clove-shaped hamon; obusa is the round part of the hamon; and juka means overlapping choji.
Several tanto (short swords or daggers) were also produced, with blades that curved inward towards the edge (uchizori) and had no ridgeline (hira-zukuri).
Late Kamakura (1288-1333) Swords
The attempted Mongol invasions of Japan in 1274 and 1281 had a significant influence on the samurai sword. Prior to the invasions, japanese samurais were used to one-on-one combat. However, the Mongols attacked in cavalry formations, wearing tough but light armors, and using weapons such as gunpowder, hand grenades and rockets, all of which were new to the Japanese.
As a result, Japanese samurai armor became lighter, and the Japanese sword also transformed. The blade became narrower, which was more effective in striking light armor than hamaguri-ba. The point became medium-sized (chu-kissaki) to allow repair in case of damage, which was impossible with ikubi. Obusa-choji and juka-choji were replaced by choji-ha based on kataochi-gunome or sugu-ha for more strength. The hi (fullers) were lowered to make room for repair lest the kissaki was broken.
During this period, the popularity of the tanto grew, and a new type was introduced. The metezashi had a curved nakago, and armored samurai wore them on the right side of their waist, hilt facing right, for quick unsheathing in the event of close contact combat.