Periods: from jōkotō to shinsakutō

The six classes

Dates shift by a year from author to author, because Japanese era names (nengō, 年号) do not line up with the Western year. Shinsakutō overlaps gendaitō: it denotes contemporary work made under licence.

Class	Dates	What opens the boundary
Jōkotō (上古刀)	to c. 900	Straight blades of continental type (chokutō, 直刀), before the curve
Kotō (古刀)	c. 900 – 1596	The curved tachi appears, and with it the five traditions
Shintō (新刀)	1596 – 1781	Keichō 1: a unified country, uniform steel, the end of classical Bizen
Shinshintō (新々刀)	1781 – 1876	Tenmei 1: Suishinshi Masahide's fukko-tō movement
Gendaitō (現代刀)	1876 – today	Haitōrei: carrying a sword is banned and the trade collapses
Shinsakutō (新作刀)	1953 – today	Forging licences return after the war

The silhouette, period by period (sugata)

A blade's outline — its sugata (姿) — is, together with the jihada and the hamon, one of the first three things a kantei looks at: it changes from one period to the next in ways recognisable even without examining the steel closely. Three things define it: where the curvature (sori, 反り) is concentrated, the size of the point (kissaki, 切先), and the width of the blade between the base and the yokote.

The position of the sori has three terms in constant use: koshizori (腰反り), curvature near the koshi — the base, by the machi — typical of Heian and early Kamakura tachi; toriizori (鳥居反り), curvature spread evenly along the whole blade, like the crossbeam of a torii gate, typical of shintō; and sakizori (先反り), curvature shifted toward the point, from the late-Muromachi uchigatana onward. The diagram summarises, period by period, where the sori moves and how the point grows or shrinks — from ko-kissaki to ō-kissaki and back to a middling size — though no real blade follows the pattern with a diagram's regularity: there are Kamakura tachi with an already fairly centred curve, and Muromachi katana with residual koshizori.

Jōkotō: before the curve

Before the curved tachi, the sword in Japan was the chokutō (直刀), a straight blade of variable cross-section — without the longitudinal ridge that would later define shinogi-zukuri — forged under direct continental influence, from the Korean peninsula and from China, which supplied both the iron and the smiths who knew how to work it. Jōkotō has no precise start — ironworking reaches the archipelago around the third or fourth century — and its close around the year 900 is not a legal date either, unlike the boundaries that follow it, but the point at which the curve becomes general and the chokutō stops being the common form.

This is the Kofun period (古墳, "tumulus") and the first centralised Yamato states: with no writing of their own until it arrives from China, no nengō until the seventh century (Taika, 645), and a record of society that is not documents but the tombs themselves. Their tumuli were furnished with haniwa (埴輪), hollow terracotta figures — warriors, horses, houses — that today are the most direct portrait of how a chief of the age was armed: laminar keikō armour, a helmet, and a straight sword at the belt, a distant forerunner of everything that would follow.

Kotō: the centuries of the great traditions

Almost everything regarded as the summit of the Japanese sword is kotō. Curvature appears in the late Heian and produces the tachi, the long blade slung from the belt edge downwards; the uchigatana, direct ancestor of the katana, becomes general in the Muromachi.

The material hallmark of kotō is variety: each region smelted its own steel from iron sand, and the result shows in the jihada (肌), the grain of the metal. That is why the gokaden — the five traditions — works for this stretch and not for the later ones. Many kotō blades reach us shortened from the tang (suriage, 磨上げ) because they were adapted to later fashions and mountings; a Nanbokuchō blade kept at full length is rare.

Heian (794–1185): the court and the birth of the tachi

The capital moves to Heian-kyō (today's Kyoto) in 794, and for much of the period effective power rests with the court and, within it, the Fujiwara clan, which rules as regents for child emperors. It is the golden age of court literature — the Tale of Genji, the poetry of the Kokin Wakashū — and of an aristocratic art, refined and largely detached from war.

But in the provinces a class grows that the court does not fully control: the bushi (武士), landed warriors whom the Taira and Minamoto houses begin to lead, and who toward the end of the period fight the first civil wars of real scale — the Hōgen War (1156) and the Heiji War (1160) — the prelude to the Genpei War (1180–1185) that closes the age. It is also when the blade curves: the straight chokutō gives way to the tachi (太刀), worn slung from the belt edge down, the work of the first smiths with names the tradition preserves — Amakuni, semi-legendary, and Sanjō Munechika and Hōki Yasutsuna, already historical, active around the tenth and eleventh centuries and regarded as the founders of the Yamashiro and Hōki traditions respectively.

The narrative art of the age survives above all in emakimono (絵巻物), painted scrolls combining text and image: the Shigisan Engi Emaki (信貴山縁起絵巻, 12th century), which tells of the miracles of the monk Myōren on Mount Shigi, is one of the few that survive painted within the Heian period itself, and it records the everyday life of the age in detail — not war, still marginal in court art; the great battle scenes of the Hōgen and Heiji would be painted later, in the Kamakura period, with the distance of someone looking back on an age that had changed the country.

Kamakura (1185–1333): the warrior shogunate and the technical summit

Minamoto no Yoritomo wins the Genpei War and in 1192 receives the title of shōgun (征夷大将軍); he sets up his government — the bakufu — in Kamakura, away from the Kyoto court, and with it the regime that will govern Japan, with interruptions, until 1868 is born: military power above imperial power. After Yoritomo's death effective command passes to the Hōjō family, who rule as regents for the shōgun for the rest of the period.

This is the technical summit of Japanese forging: the five traditions of the gokaden — Yamashiro, Yamato, Bizen, Sōshū and Mino — become fixed, and Bizen, with access to regional iron and steady demand, becomes the country's largest producer. Mid-century the blade widens and the point shortens — the so-called ikubi-kissaki (猪首切先), "boar's-neck point" — before returning toward the end of the century to a more slender chū-kissaki.

The event that marks the period is the Mongol invasions: Kublai Khan sends two fleets, in 1274 and 1281, and both fail — the second wrecked by a typhoon tradition named kamikaze (神風), "divine wind". The war against an unfamiliar enemy, with tactics and weaponry unlike those of Japanese civil war, is recorded in the Mōko Shūrai Ekotoba (蒙古襲来絵詞), the painted scroll the warrior Takezaki Suenaga himself commissioned around 1293 to document — and claim reward for — his part in the battle; it is one of the very few contemporary, not retrospective, visual sources of a Kamakura samurai in combat, with tachi, bow and armour as they were actually used.

Nanbokuchō (1336–1392): the outsized blades

In 1336 Ashikaga Takauji breaks with Emperor Go-Daigo and enthrones a rival: for close to sixty years two imperial courts coexist, the Northern one in Kyoto, backed by the Ashikaga, and the Southern one, exiled in Yoshino — hence Nanboku-chō (南北朝), "Northern and Southern Courts". It is a period of almost continuous war between the two courts' supporters, resolved in 1392 when the South accepts reunification under the Ashikaga shogunate, by then settled in the Muromachi district of Kyoto.

Demand for weapons drives up production, and its scale too: tachi and nagamaki are forged up to 90 and 100 cm long, with the longest point the Japanese sword ever produced, the ō-kissaki (大切先). These are blades meant for combat on foot and on horseback against masses of infantry, not for ceremonial use; the vast majority that survive today have been shortened at the base (ō-suriage), because their length stopped being practical once tactics and fashion changed, and many lost their signature in the process.

From the armour of the Nanbokuchō–Muromachi transition — yoroi of laminated plates, coloured silk cords marking the clan, a kabuto helmet with riveted rows — complete pieces survive in museums: together with the blade itself, they are the object that best conveys the scale of the warrior who carried these swords.

Muromachi (1392–1573): mass production and Noh theatre

The Ashikaga shogunate, based in the Muromachi district of Kyoto, never manages to control the whole country: after the Ōnin War (1467–1477), which devastates the capital, central authority dissolves and the Sengoku jidai (戦国時代), the "age of the country at war", begins, with provincial lords — daimyō — in almost constant conflict well into the following century.

Permanent war changes the sword twice over. First the mounting: the uchigatana (打刀), worn edge-up thrust through the obi instead of slung from the belt, displaces the tachi because it draws faster, and its curvature shifts toward the point — the sakizori of the diagram above. Then production: workshops in Bizen and in Seki, in Mino, mass-produce blades of modest quality and low price for ashigaru armies, the peasant infantry raised in bulk; this output is known as kazu-uchimono (数打物), "things made by the count", and coexists with commissions of far higher quality for samurai of rank. A Bizen blade signed and dated 1526 by the smith Masazane, today in a public collection, is an example of the care a recognised master still gave his work in the middle of an age of mass production.

Despite the war, it is also the century of Noh theatre (能), perfected by Kan'ami and his son Zeami under shogunal patronage, and of the wabi-cha tea ceremony fixed by Sen no Rikyū: the same daimyō who financed a company of ashigaru with kazu-uchimono swords could be the patron of a Noh troupe or a collector of tea utensils.

Why 1596

The line between kotō and shintō is drawn at Keichō 1 (1596), and it answers to no decree but to several changes converging:

• Toyotomi Hideyoshi unifies the country: the iron and steel trade centralises and the metal stops being local, so the jihada turns tighter and brighter and loses its regional character.
• Imported iron arrives through trade with the Portuguese and the Dutch, the so-called nanban tetsu (南蛮鉄).
• Bizen production, the largest in the country, collapses after the great flood of the Yoshii river in the Tenshō era (around 1590); the methods and the smiths of Mino spread across Japan.
• The mounting changes: the uchigatana displaces the tachi, and blades are forged as daishō pairs, with more uniform outlines.

Two labels are in constant use within shintō: Keichō-shintō (1596–1624), broad blades imitating the Nanbokuchō, and Kanbun-shintō (c. 1661–1673), with very shallow curvature, a chū-kissaki point and a regular hamon — the most recognisable pattern of the early Edo.

Shintō (1596–1781): the Edo peace and its imagery

In 1603 Tokugawa Ieyasu receives the title of shōgun and founds in Edo (today's Tokyo) the government that will unify and pacify Japan for two and a half centuries: sankin-kōtai forces daimyō to reside alternately in Edo, keeping their power in check, and the country closes itself off almost entirely from the outside world from the 1630s (sakoku, 鎖国), with Nagasaki as the only controlled gateway for trade with the Dutch and the Chinese.

Without civil war, the sword changes function: it remains the badge of samurai rank — from 1588, with Toyotomi Hideyoshi's "sword hunt" (katanagari), and more rigidly under the Tokugawa, carrying two swords at once, the daishō, becomes a class privilege reserved by law — but it stops being forged chiefly for war. It settles into a more uniform blade type — toriizori, chū-kissaki, tighter jihada from already-centralised iron — and the signature gains aesthetic prominence: with less real combat to demonstrate, a smith's reputation and the calligraphy of his mei matter more than before.

Peace also grows an urban culture the art of the time depicts with relish: the Rakuchū Rakugai-zu (洛中洛外図), pairs of folding screens painting panoramas of Kyoto — temples, processions, shops, people of every station — is a genre that comes into fashion right at this start of the Edo period, and dozens of versions survive in museums worldwide; shortly after, ukiyo-e will begin, the print of the "floating world", documenting kabuki theatre and pleasure districts with the same detail these screens bring to the city.

Why 1781

The shinshintō boundary carries a name: Suishinshi Masahide (水心子正秀, 1750–1825), born in Dewa province and working in Edo in the service of the Akimoto house. Convinced that shintō had lost its way, he preached a return to Heian and Kamakura technique — the fukko-tō (復古刀) movement — and spread it through his writings and a workshop that trained dozens of pupils.

What follows is a century of revival: blades deliberately reproducing the Sōshū, Bizen or Mino work of the kotō, in very clean, tight steel, often with a long point in the Nanbokuchō manner. Military demand in the Bakumatsu, the turbulent years before 1868, sustains output and produces figures such as Taikei Naotane and Minamoto Kiyomaro.

Shinshintō (1781–1876): revival and the Bakumatsu

The country's seclusion breaks in 1853, when the American commodore Matthew Perry forces the ports open with a show of naval force; the following decade, the Bakumatsu (幕末, "end of the shogunate"), brings growing political violence between the faction defending the Tokugawa shogunate and the sonnō jōi movement (尊王攘夷, "revere the emperor, expel the barbarian"), which demands the restoration of imperial power and the country's re-closure.

After a century of peace, demand for swords meant for real combat — not for ceremony — picks up again, and with it the prestige of the shinshintō forging that Suishinshi Masahide had begun. The Boshin War (1868–1869), which pits the shogunate's supporters against imperial forces and ends with the fall of the Tokugawa and the Meiji Restoration, is the last conflict in which the Japanese sword is used on a large scale as a conventional weapon of war: the following years will reduce it to a symbol, first by law and then simply through the replacement of firearms.

1876 and 1953: when the law decides

On 28 March 1876 the Meiji government issued the Haitōrei (廃刀令), banning the wearing of swords in public except by the military, the police and former lords. The trade collapsed: many smiths turned to knives and tools, and the few who survived did so on ceremonial commissions. Gassan Sadakazu is the extreme case of success in that desert: in 1906 he was appointed an Imperial Household Artist (Teishitsu Gigeiin, 帝室技芸員).

After 1945 the occupation ordered swords to be surrendered and production stopped altogether; the intervention of Japanese scholars saved the blades of artistic merit, and in 1948 the NBTHK was founded. In 1953 the Japanese cultural-property authority began issuing forging licences again, and shinsakutō starts there. Today forging requires a licence, every blade is registered, and each smith's output is capped by regulation.

Between 1876 and 1953, within the gendaitō class itself, two worlds coexist: on one hand a handful of masters with artistic or ceremonial commissions — Gassan Sadakazu among them; on the other, from the 1930s and especially during the Second World War, the semi-industrial production of military swords (guntō, 軍刀) to equip imperial army officers, far removed in technique and intent from traditional forging even though often mounted to look samurai.

Shinsakutō (1953–today): licensed forging

Since 1953, forging a sword in Japan has required a licence from the Japanese cultural-property authority, granted after formal training — typically several years under an already licensed master — and an examination; the number of blades each smith may produce per year is capped by regulation, and every one must be registered before it leaves the workshop. The declared aim is not mass output but preserving the craft as heritage: in 1963 Miyairi Akihira is designated a living national treasure (ningen kokuhō, 人間国宝), the second smith to receive the title after Takahashi Sadatsugu.

Shinsakutō (新作刀), "newly made blade", tends to look backward: many contemporary smiths work deliberately in the style of a kotō tradition — Bizen, Sōshū, Yamato — or reproduce shinshintō traits, and the NBTHK holds a new-work competition every year (Shinsaku Meitō Ten) that is today the chief way the craft is recognised within a smith's own lifetime.

From Heian to Shōwa

The sword world treats the Nanbokuchō as a period of its own and reserves "Muromachi" for 1392–1573, even though in general history the Muromachi shogunate begins in 1336.

Period	Dates	What happens to the blade
Heian (平安)	794 – 1185	From the straight blade to the slender curved tachi; Munechika, Yasutsuna, Ko-Bizen
Kamakura (鎌倉)	1185 – 1333	Technical summit; broad blades with short points mid-century; the Sōshū is born
Nanbokuchō (南北朝)	1336 – 1392	Enormous blades with long points (ō-kissaki); today almost all heavily shortened
Muromachi (室町)	1392 – 1573	The uchigatana with high curvature prevails; mass production in Bizen and Seki
Azuchi-Momoyama (安土桃山)	1573 – 1603	Keichō-shintō: copies of the Nanbokuchō, with steel already uniform
Edo (江戸)	1603 – 1868	Shintō and shinshintō; the sword as a badge of rank more than a weapon
Meiji (明治)	1868 – 1912	The Haitōrei of 1876; the trade all but disappears
Taishō (大正)	1912 – 1926	Study and appraisal are systematised; the gokaden takes its present form
Shōwa (昭和)	1926 – 1989	Military swords, the 1945 ban, the 1953 licences and shinsakutō

Main nengō at a glance

A date cut into a tang almost always carries an era name (nengō, 年号), not a Western year: this table gathers the eras most often cited when dating a Japanese blade, with the class they belong to and what makes them recognisable.

Nengō	Years	Class	What that era is associated with
Kōan (弘安)	1278–1288	Kotō	The Mongol invasions
Ōei (応永)	1394–1428	Kotō	Early Muromachi; abundant dated output
Bunmei (文明)	1469–1487	Kotō	The Ōnin War and the start of the Sengoku
Tenshō (天正)	1573–1592	Late kotō	Hideyoshi's unification; the boundary with shintō
Keichō (慶長)	1596–1615	Shintō	Start of the class; Keichō-shintō
Kanbun (寛文)	1661–1673	Shintō	The Kanbun-shintō outline, almost without sori
Genroku (元禄)	1688–1704	Shintō	The height of Edo's urban culture
Tenmei (天明)	1781–1789	Shinshintō	Start of the class; Suishinshi Masahide
Bunka–Bunsei (文化・文政)	1804–1830	Shinshintō	The fukko-tō movement in full swing
Kaei (嘉永)	1848–1854	Shinshintō	On the eve of Perry's arrival
Keiō (慶応)	1865–1868	Shinshintō	The Bakumatsu and the Boshin War
Meiji (明治)	1868–1912	Gendaitō	The 1876 Haitōrei
Shōwa (昭和)	1926–1989	Gendaitō / shinsakutō	Guntō military swords; the 1953 licences
Heisei (平成)	1989–2019	Shinsakutō	Contemporary licensed forging

How to read a date on the tang

The date, when there is one, is cut on the side of the tang (nakago, 茎) opposite the signature and almost always runs era, year, month: 嘉永四年二月 is "second month of Kaei 4", that is 1851.

• Year 1 of an era is the year it was proclaimed, so the sum is "first year + n − 1". The first year is usually written 元年 (gannen).
• 吉日 (kichijitsu, "auspicious day") closes many dates: forging takes more than a day, and a smith rarely records a particular one.
• The sign of the sixty-year cycle (eto, 干支) is often added, confirming the year twice over.
• Until the switch to the Gregorian calendar in 1873 the months are lunar: the "second month" is not February.
• There are scribal oddities: 亖 or 二二, "four" written as four strokes, is the most quoted.
• Only a minority of blades are dated. A date in the smith's own hand is first-rate evidence, but signatures and dates were also faked (gimei, 偽銘) or added later in inlaid gold (kinzōgan-mei, 金象嵌銘) when an unsigned blade was attributed.