Swords made during the Heian period (794-1185) through the late Muromachi Era (1573-1599) are called Koto, and are classified in terms of the Gokaden, the five schools that developed in the provinces of Yamashiro, Yamato, Bizen, Soshu, and Mino. During the Koto period, the features of the jigane varied significantly because of the different materials used in each province. Swords made during this period can be recognized by the forging style, often down to the specific smith.
Heian Era (794-1184)
When Kammu Tenno came to power, he moved the capital from Nara to Kyoto. The whole era was characterized by the prevalent tendency toward japanizing the Chinese influences that had come over the sea during the previous centuries. The method of forging a sword with a softer inner core wrapped into a harder steel one was developed during this period.
The most ancient swords with this feature belongs to the Ko-Bizen tradition and are dated around 950 A.D. This is the time which is going to change to a Samurai government ( Genji and Heike ) from an aristocrat government. After the war happened in the middle stage of Heian Era, the battle style changed. That is, they began to fight on horseback. There is an ancient legend that attributes this revolution in sword making to Amakuni, traditionally believed to be the maker of Kogarasumaru or ‘Little Crow’, the first curved Nippon-to, now in the Imperial Household Collection. According to this legend Amakuni was the Emperor’s swordsmith. One day he saw his lord’s army returning from a battle, and the Emperor ignored him instead to give the usual cheers for the good work made with the blades. Then he noticed that many soldiers had broken swords. They were chokuto or straight swords. He was so disappointed with this that he avoided eating food and drinking water for a week, studying a better way to make swords.
According to the legend Inari, the Kami of swordsmakers, appeared in a dream to Amakuni, teaching him how to wrap a soft steel core in a harder one, and how a curved edge is more suitable to cuts and more resistant to shocks than the previous straight one. The day after Amakuni made Kogarasu Maru, the ancestor of all Nihonto.
Heian was the era of tachi. In this period it became customary to sign the blades. The oldest signed blade is probably one tachi forged by Sanjo Munechika. The oldest tachi with date as well as the name of the smith engraved on the tang is from 1159 and was made by Naminohira Yukimasa. The shape of a Japanese sword (tachi) in this age the mihaba (width) near the nakago is wider than that near the kissaki. Kissaki are small (ko-kissaki) and sori (curvature) looks like it suddenly fell to the ridge side at right above the nakago. But sori near the monouchi is little. This shape is refined in a sense. Hawatari (length) is about 75/80cm. This size is suitable for chopping at the enemy on the ground while riding on Japanese horses. The horses in this age were not like present ones, but were small and massive. Moreover, it fit to stab the enemy on the ground because the curvature near the point is little and nakago (tang) is short compared with the rest of the blade. Hamon is sugu, straight.
During the Heian era, two clans, the Minamoto (Genji) and the Taira (Heike), grew in power and importance. The end of the era is marked by the battle in Dan-No-Ura, where these two clans clashed together. We have to remember another legend, still being debated, that in this battle was lost the Ancestral Sword, Kusanagi-no-Tsurugi, part of the ‘Three Jewels,’ the most important treasure still in possession of His Imperial Majesty. This ancestral sword was found into the tail of a dragon by the kami Susa no O no Mikoto, and was, together with the mirror and the claw-like jewel, the symbol of the Imperial Power. According to this legend, it was substituted with another sword, the same we can see in the Imperial Treasure today, other sources said the sword lost was a fake, and the original one still remains in the Imperial Treasury.
Kamakura Era (1184-1333)
After defeating the Taira clan at Dan-No-Ura, Minamoto no Yorimoto moved his shogunate to Kamakura. Emperor Gotoba, the formal ruler, remained in Kyoto. This also marked the beginning of the rule of the Samurai class. Kamakura became the cultural capitol, and swordsmiths from all over the country gathered there. These are the days of Masamune and his Jittetsu (ten disciples). Today it is generally agreed that the best blades were made in this period and, for quality and beauty, still remain at the top.
Kamakura sword-making can be divided into three sub-periods :
Early Kamakura (1184-1231)
In this period, the Kamakura shogunate and court nobles in Kyoto scrambled for political power. And internal troubles broke out in the Kamakura shogunate. Therefore, demand for swords increased all over the country. This period is a transitional period from the refined shape in the last stage of Heian Era to the mighty shape in next period. Sori does not look like suddenly fall to the ridge side at right above the nakago, and the center of the sori moved upper in comparison with the previous period. This type of sori is called koshi-zori. It means the sword is curved at waist of the blade. The width near the kissaki (monouchi) is not so different from that near the nakago (habakimoto), and the kissaki became a little longer. A standard length of this period is about 79cm. Hamon in this period is based on sugu-ha, straight. The swords until this period are made in ko-nie. Swords made in nioi did not exist yet.
Middle Kamakura (1232-1287)
After the war happened in 1232, the Hojo family held real power, and the Kamakura shogunate reinforced their authority. Kamakura became the center of Samurai culture and the demand for swords increased. The Kamakura shogunate called in some swordsmiths who had superior skill from Kyoto and Okayama. They moved with their entire families, and Kamakura became the central location for the production of swords.
The shapes in this period did not remain copies of the older period, but changed to be more massive. The width became greater, with is no difference between the width near the kissaki and near nakago. The blade thickness also became greater. Moreover, kissaki became to be Ikubi and the edge came to be hamaguri-ba because the edge became thicker. Hamaguri means a clam, and we call it this because the cross-section of the blade looks like a clamshell. Sori is still koshi-zori, and the center of sori moved more upper, and the nakago became a little longer than those of the former period.
In the hamon, the brilliant patterns became to be conspicuous. Especially Fukuoka-Ichimonji school in Bizen (Okayama prefecture) made the so-called Obusa-Choji or Juka-Choji and they became popular. Obusa means the shape of the head of hamon (round part of hamon) looks like a big bunch of choji, and juka means choji overlapped each other. And a lot of tanto started to be made during this period. The characteristic is hira-zukuri and they curved toward the edge. That is, the blade curved contrary to the normal . We call this curvature uchi-zori or takenoko-zori. But originally the blades were straight, and the thin edges were polished again and again, then the width of the edge decreased. Therefore, blades look as if they curved the reverse way. Hawatari is about 25cm.
Late Kamakura (1288 -1333)
The Mongolian invasions attempt of 1274 and 1281 greatly influenced the Japanese sword. Until this period, the method of battle in Japan was based on single duels, with rituals as exchanging names and genealogies each other before fight with no organized formations and tactics. On the contrary, Mongolians attacked suddenly in organized formations following tactics. Moreover, their armor was extremely tough, and they used weapons which Japanese have never seen before, including gunpowder hand-grenades and rockets. Their armors were light and they could move fast.
After that, the Japanese armor became lighter and the sword's shape changed to make it capable of chopping the light armor without being entrapped and then broken in them. The former blade was hamaguri-ba. When you chop a hard thing, hamaguri-ba is suitable, but the armors began to be light and thin in this period. So the blade in this period became thinner compared to the one of the former period. Kissaki became to be chu-kissaki (medium length); that is, kissaki got longer because when ikubi-kissaki was damaged, no room for restoration was available. When you stab the enemy, chu-kissaki is suitable. Ikubi-kissaki was wider then chu-kissaki. Mihaba (width) became narrow. This shape looks like the refined one of the first stage of Kamakura, but kissaki in this period are bigger and the center of the sori moved up. In this way, if the edge became too thin, strength of the blade decreased. Therefore, Mihaba became wider, and if Mihaba become wide, the kissaki had to becme longer. The peak of this change was in Odanbira in the Northern and Southern Dynasties.
The Mongolian Invasions influenced hamon, too. Obusa-choji and juka-choji gave way to choji-ha based on sugu-ha or kataochi-gunome, because the blade with very wide ha is easy to break. Swordsmiths realized it from experience. Ha is harder than the other parts, so if the harder part is the majority of the blade, the blade is easy to break because it can not absorb the shock. And the top of hi (grooves) invariably stop lower. This is made to leave room for repair when the kissaki was damaged.
In this period, tanto increased in number and there is characteristic shape. That is, their nakago is curved. This tanto is called "mete-zashi." Samurai wore this tanto when they donned armor and they put it on the right-side of their waist, handle facing right to be easy unsheathed when armor were in contact with each other; in grappling, close combat is expected. This mete-zashi is to stab enemy through a crevice of armor, so the mihaba is narrow.
Nambokucho Era (1334-1393)
Emperor Godaigo in 1334 started a rebellion to overthrow the shogunate in an attempt to restore the power of the imperial court, & he gained the control of the country. But after only two years, Ashikaga Takauji raised his own Emperor (Komyo) to power. The power split in two courts: Godaigo held court in Yoshino, and Komyo built his government in Kyoto. The north (Nan) and south (Hoku) courts fought for nearly 60 years giving the name to this period: ‘the Courts of the South and of the North.’
Years of continual war raised the need for swords & changed blade shapes. The method of battle changed to between group and group. The battle formation was foot soldiers surrounding a leader riding on a horse. As footsoldiers increased in importance, a very long sword, more suitable for this new horseback fighting-style, was created. The long tachi was for driving away the enemy, with lengths from 85cm to over 1m. Some Odachi or Nodachi or Odanbira were 120-150 cm. The longer ones were used by footsoldiers to cut horses' legs and open gaps in enemy spearmen lines.
Mihaba of these tachi was wide, so the kasane was thin to lighten the weight, characteristic in this period. Therefore, when looking at Nambokucho tachi, if Kasane is thick, doubts about authenticity arise. As mihaba grew wide, the kissaki came to be longer as a logical consequence (o-kissaki). This type of sword was too long to wear, so the Samurai on horse gave his odachi to a follower to carry, who drew it when needed. Therefore, if the follower was killed or driven away, the tachi became useless. This is the reason a smaller tachi (kodachi) was carried hanging from the obi of the armor.
This need was another reason for the rise of the uchigatana that began to be made in this period. The length is about 70 cm and it was used together with the longer tachi. All blades followed the fashion to be large like tachi. Tanto in this period have a peculiar characteristic: the length is about 35cm and they were shaped as hira-zukuri. Mihaba is wide and kasane is thin; they curved at middle of the blade. They are called sunobi tanto, and they remain tanto although for their length they should be called wakizashi.
Naginata and yari became longer as well to fight against this longer tachi. Fighting on a horse became disadvantageous. These too-big blades all disappeared shortly after the end of the period. In effect, the matter was formally resolved in a compromise, but Ashikaga and the Northern Court were the factual winners. Some suggest that some schools related to the Southern Court became extinct because of the defeat (i.e., the Hosho school founded by Sadamune, son of Masamune), but no strong evidence is given.
Hamon in this period is notare or hitatsura. Due to their geometry, Nihonto in this period were generally believed to have the sharpest blades ever. This is one reason that in the Edo period, many of these long tachi were shortened to katana size to fulfill the Shogun edicts about swords length. The same happened to nagamaki, naginata, and sometimes even to omiyari.
Muromachi Era (1394-1595)
After the dynastic war, a short period of peace followed. But the Ashikaga Shogun was “de facto” powerless, and the true power was held by the Daimyo. This very dangerous situation unavoidably left room for troubles. The battle for the true power began in 1467 with the so-called Onin-war that started the Sengoku-jidai - 'the age the country at war.' The whole country was in a constant state of war for almost a hundred years, until Oda Nobunaga, Toyotomi Hideyoshi, and finally Tokugawa Ieyasu managed to gain power, and pacify the country.
In the Muromachi Era, Samurai gradually began to use uchigatana instead of tachi. They still used tachi in this time, and the shape looks like the first stage of Kamakura Era; that is, mihaba is narrow and kissaki is small. But the sori is different. In Kamakura Era, the center of the sori is near the nakago or little upper, but the center of sori in Muromachi Era moved ahead. Curved around monouchi, the last part of the blade toward the point, is a characteristic often found in swords of the Muromachi Era. This curvature is called saki-zori.
This is a transitional period from tachi to katana, so starting from this era, it is hard to distinguish between the two types. Swordsmiths made both, and often the shape is not enough to tell the difference. The only way to distinguish in between is to observe the mei, the swordsmith’s signature. The mei must face out from the body when worn. Tachi were worn edge-down and uchigatana edge-up. So the position of the mei on the tang tells us which type of blade it is. If no signature is present, the difference is often merely in the mounting type. The sword types of this era can be divided into three groups:
Early Muromachi (1394-1466)
As the armies grew, mounted soldiers became ever rarer, and the main force of armies consisted of foot soldiers. Even if many tachi were still made, the time of the katana was already dawning. Shorter blades were easier to carry and faster to draw. The center of curvature of the blade moved to the center as the blades were increasingly designed for a fast draw and to be used on foot. Most swords were 69.7 to 72.7cm in length, and narrowed towards the point.
Middle Muromachi (1467-1554)
As the mobility of troops became strategically more important, the swords got even shorter. Most swords manufactured during this period were 60-65cm long and had the same width all the length of the blade. Such blades were suitable for chopping with one hand and for quick-draw. These katana are referred to as katate-uchi. Katate means one-hand. There is no difference of width between monouchi and habakimoto, and the shape has a strong appearance. Nakago became to be short to be suitable for one-hand grip. The katana was quickly replacing the tachi.
The ever-increasing need for swords also meant that not all swords were manufactured to the same high standards as before. The term kazu-uchimono or taba-gatana was used to denote the mass-produced swords from the quality swords. Kazu-uchi means mass-produced, and taba-gatana means they were sold in a bundle, as such swords were sold this way inside Japan and exported to Ming-dynasty China in their tens of thousand. These swords are disliked by collectors due to their low quality, but this doesn’t mean that they weren’t very effective.
Wakizashi also started to be made, with lengths of about 40cm. They were made in hira-zukuri and have no sori. Shinto deities and Buddhas or Sanskrit characters were often engraved on the blade; these engravings are called horimono. This type of wakizashi is characteristic of in this period. A particular type of tanto, called yoroi-doshi (armor-piercing) began to be made. Yoroi-doshi is to stab enemy through an armor crevice, and so the cross-section is triangular, very thick but not broad, with a very strong, relatively short kissaki.
Late Muromachi (1555-1600)
In the 12th year of Tenmon, A.D. 1543, the face of warfare in Japan was changed forever. In this year, the Portuguese first introduced firearms to Japan, named tanegashima teppo from the isle in the southern Kyushu where the first Portugueses casually landed. Japanese Daimyo immediately realized the potential of such a weapon.
A teppo is very effective and needs much less training than for a sword of Japanese sow. Even if the early guns were not accurate and took a long time to reload, Oda Nobunaga used them very effectively in the battle of Nagashino in 1573. The mounted troops of the Takeda clan - considered to be the finest in the country and invincible - were heavily beaten by men who were simple Ashigaru, farmers trained to use gunlocks. The mounted troops were powerless. The battlefield belonged to tight formations of footsoldiers armed with guns. Some armor became heavy and thick to protect from bullets. In the meantime, swords became longer, heavier, and more robust, lacking in elegance. After the death of Oda Nobunaga, the country was unified under Toyotomi Hideyoshi, and Sengoku-jidai started its last run.
In the late Muromachi, we find the artistic revolution of the Momoyama Era, when the katana finally replaced the tachi as the main sword of the Samurai. The difference between a tachi and a katana is, to make an incredibly difficult explanation as simple as possible, the position of the mei. The swordsmith's signature must be on the part of the blade that faces outside, so as the tachi is worn edge-down and the katana is worn edge-up, the signatures are placed in opposite positions. In absence of a signature the mounting is often the only difference between the two types of swords. Obviously this change was more a slow evolution rather then a sudden revolution. So we have a lot of blades that are "in between" that can't be easily put in a specific category.
The wearing of daisho (daito/shoto,long/short sword, meaning katana and wakizashi) began in this period. Basically, a backup blade was always carried by Samurai, but the fashion of having a matched pair of mountings for main and backup sword started here. This is a very crucial change in the Japanese sword history. To explain the (slow) switching from the ancient fashion to the new one we need to address the meaning of the term wakizashi. It's made by two words waki" (side, secondary) and "zashi" (from sasu, "to insert"). In the sword context it, means "to insert between the obi" a sword to be worn inserted between the folds of the obi.
Tachi requires another verb, "haku," to wear "hanging" from the waist. Backup swords were carried by Samurai from the very beginning of their history, and they were usually inserted "between the obi," so wakizashi in ancient times referred to any sword that was secondary to the tachi and worn inserted in the obi with no reference to its length. In Koto times, back-up blades spread from yoroi-doshi to chiisa-gatana (shorter than katana) and koshi-gatana, all always worn inserted in the obi except the Koshigatana, that sometimes was worn hanging from obi.
The length, in these times, wasn't an issue to qualify a blade as "wakizashi" and the term "daisho" (pair of long and short swords) wasn't yet in use. There is a document quoting that Oda Nobunaga wore (with the Kanji used for the meaning "inserted between obi") a set of Daisho. So it is safe to assume that between Tenbun and Eiroku (1532-1569), this fashion was adopted by Samurai, most likely having already been adopted by lower-ranked troops sometime earlier. It was during the Momoyama that the first official criteria were published to differentiate types of swords according to their length, creating the categories we find later on, and imposing who was allowed to wear what type of sword, but these regulations weren't really fully applied. But strict regimentation was only a matter of time.
In Shoho 2 (1645), "The Order Regarding Dai-Sho Katana and Hair Style" fixed the maximum length of katana to be 2 shaku and 8 to 9 sun (84.84 cm - 87.87 cm), and wakizashi to be 1 shaku and 8 to 9 sun (54.54 cm - 57.57 cm). In Kanbun 8 (1668), the Tokugawa Shogunate issued the famous Muto Rei (No Sword Order), a law that firmly prohibited the commoner class from carrying or wearing any sword longer than ko-wakizashi (small wakizashi) unless specifically permitted by the government. According Muto Rei, ko-wakizashi" is defined as a sword with blade length shorter than 1 shaku and 5 sun (45.54cm).
Others edicts followed to fix blade lengths for high-ranking Samurai and Hatamoto when on duty in Edo, and in the mid-Edo period we can find what is generally accepted as the today's standard lengths for Japanese swords blades :
Tanto - to be shorter than 1 shaku (= 30.3cm)
Wakizashi - to be from 1 shaku (= 30.3cm) to 1 shaku 9 sun 9 bu (= 60.297cm); but more specifically:
Ko-Wakizashi - to be from 1 shaku (= 30.3cm) up to 1 shaku 4 sun 9 bu (= 45.147cm);
Chu-Wakizashi (mid-size wakizashi) to be from 1 shaku 5 sun (= 45.45cm) to 1 shaku 7 sun 9 bu (= 54.237cm), and
O-Wakizashi (i.e., large size wakizashi) - to be from 1 shaku 8 sun up to 1 shaku 9 sun 9 bu (= 60.297cm);
Katana - to be 2 shaku (=60.6cm) and longer.
Blade lengths are always measured in a straight line between the munemachi and the tip of the kissaki.
Since the official adoption of the metric system in 1891, the traditional length units of "shaku," "sun," and "bu" are no longer used. The legal designations of tanto, wakizashi, and katana by their lengths under today’s Japanese laws are as follows :
Tanto - to be 30cm or shorter;
Wakizashi - to be longer than 30cm but shorter than 60cm;
Katana (and tachi) - to be 60cm or longer
This legal classification sometimes doesn't match with the academic one that is more complex, implying the way in which the blade was originally intended to be worn (tachi or katana) and its purpose. Academically speaking a sunnobi-tanto, is so-called because it is always a little longer than one shaku (30.3 cm) is these days legally speaking a wakizashi.
JAPANESE SWORD SOCIETY OF HAWAII 2011