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Late Heian (987 - 1185) early Kamakura period (1185 - 1231)
The shinogi zukuri tachi came into existence. In addition to the ridges (shinogi) incorporated into the structure, there was a marked difference (50 - 65%) between the width at the tip (sakihaba) and the width at the base (motohaba).
The curvature was deep koshizori (curve is emphasized at the base) mostly between the range of 2.7 to 3.0cm, and fumbari forming a strong stretching line toward the back of the point. They had ha-watari or 'nagasa' (length) originally of about 85cm
Late Heian blades had ko kissaki, a wide motohaba, narrow sakihaba. The early Kamakura blades were little different from those of late Heian however they tended to have a larger kissaki and the sakihaba was a little wider, a slighhtly 'grander' blade shape.
Jokoto - Ancient times (pre 987)
Refereneces for this earliest period in sword's history are found among those excavated from ancient burial mounds (4th - 9th cenuries) and the treasures preserved in the Shosoin built in the Nara period (8th - 10th centuries).
These prototypes of the Japanese sword had no curvature, and were mostly formed in hira - zukuri (flat, ridgless) or in kiriha - zukuri (longitudinal ridge parallel and close to the cutting edge).
Periods
Mid Kamakura period (1185 - 1287)
A most stately tachi form consisting of ample thickness (kasane), little tapering in blade width towards the point (sakihaba), wide motohaba, compact chu or ikubi kissaki, and full hira - niku (ample convex curvature of the ji surface) .
The shinogi is placed slightly more towards the mune. The blade is still koshizori but the upper part of the blade maintains curvature (sometimes described as 'toriizori, tending towards koshizori').
Jokoto (pre 987) Momoyama (1596 - 1624) Jokoto pre (964)
Heian  (794 - 1185) Edo (1600 - 1867) Koto (987 - 1596)
Kamakura (1185 - 1333) Meiji (1868 - 1912) Shinto (1596 - 1780)
Nanbokucho (1333 - 1392) Taisho (1912 - 1926) Shinsnhinto (1781 - 1876)
Muromachi (1392 - 1573) Showa (1926 - 1989) Gendaito (1876 - onwards)
Azuchi-Momoyama (1573 - 1600) Heisei (1989 - )  
Late Kamakura period - early Nambokucho (1288 - 1337)
Blade shape became even more sturdy and stately with a marked and uniform width throughout its length. (Note: some returned to the slender late Heian structure  however the degree of sori in upper part of blade increased). Chu kissaki which is somewhat long and either koshizori or deep torizori. The ha-watari originally about 90cm
Gunome and notare temper patterns begun to appear. Later, possibly due to the influence of Masamune who was active in Soshu during this period (and who had perfected the nie deki style of swordmaking), nioi structured temper patterns became more nie dominant.
Mid to late Nanbokucho period (1338 - 1391)
This period features extraordinarily long tachi measuring over 90.9cm (3 shaku), some o-dachi were longer than 120cm. They were all made thinner (kasane) and some had bo-hi engraved to reduce the weight. They had a wide mihaba with little difference in the sakihaba (little tapering). Other features are, O-kissaki and a fukura which is not rounded (kamasu), shallow torizori, a high shinogi, narrow shinogi ji, and hira niku which is not full. Many of these have been shortened to katana length or to a ha-watari of less than 75cm, and it is important to remember that shortened tachi will look very different from their original form.

Later Nanbokucho blades were the same as mid Nanbokuchu however the sakihaba in particular is narrower, and chu kissaki are common.

The hamon was often a large notare ba (spaciously undulating zig zag) to match the large proportions of the blade, a new unique temper of hitatsura (covering all of the blade surface) was sometimes applied.
Muromachi period (1392 - 1572)
Early (1392 - 1428): Early Kamakura style of sword making was revived, shinogo zukuri tachi or katana with a deep torizori tending towards sakizori, a narrow sakihaba, and chu kissaki. Around 72.7 - 75.7cm in length.
Mid (1429 - 1466): Changed slightly with a narrower mihaba (blade width) in combination with a wide motohaba (width at the machi). Added to this was a thick kasane.
Late (1467 - 1572): Shinogi zukuri katana or 'uchi gatana' with a ha-watari of not much more than 60cm. The sori was far more outstanding towards the tip than the base (deep sakizori), chu kissaki, rounded fukura, rather wide mihaba with little tapering . The nakago (tang) was made short to suit one handed fighting styles. At the end of the Muromachi period some ha-watari of about 73cm can be seen. Due to the incessant warring at the time (Sengoko period - warring states) katana production could hardly keep up with demand and therefore a large number of mass produced inferior blades were made. These are called kazu - uchi. There were some well made blades usually with the makers signature and date completed in their own hand, these custom made blades are called chumon-uchi.
Azuchi Momoyama/Momoyama period (1573 - 1643)
Shinogi zukuri katana with a shallow sori, wide mihaba with little tapering and generally a long chu kissaki or o-kissaki with a kasane that is in proportion. The sugata tended to be similar to a shortened tachi of the Kamakura or Nanbokucho periods (without fumbari). The ha-watari of this period was of about 75cm and the overall blade structure is most powerful. Katahiriha-zukuri swords were also particularly fashionable during this period and made by Myoju, the Horikawa school and the Yasatsugu school.
Early (1644 - 1687) - Mid Edo period (1688 - 1780)
Early Edo: Shinogi zukuri katana with a remarkably shallow sori, normal width (mihaba) a marked tapering towards the tip. The kissaki was medium sized and the ha-watari of this period was generally around 69cm. This structure can be seen most in blades from the Kanbun and Empo eras and is known as 'Kanbun Shinto'. The daisho became the object of official regulation and the wakizashi of around 45 - 54cm became the sho of the pair.
Mid Edo: Ha-watari slightly longer than Kanbun Shinto, deeper sori and chu kissaki.
Late Edo period (1781 - 1876)
Shinogi zukuri katana with a deep sori, normal width (mihaba). The kissaki was medium sized and the ha-watari of this period was generally around 75cm.
Blades made after the Bunka (1804-1818) and Bunsei (1818-1830) eras are referred to as fukko-shintõ (revival swords). Pioneers of the revival movement include Suishinshi Masahide and Nankai Taro Tomotaka. Taikei Naotane was among Masahide’s students. Minamoto Kiyomaro led a revival aimed at soshu-den and Mino-Shizu workmanship. Bakumatsu blades are shallow in curvature, have a wide haba with not much difference in width between the saki and moto-haba, and are around 75.7cm-78.7 cm in length, with an o-kissaki and thick kasane.
Meiji period onwards
Blades made from the 9th year of Meiji until present day are referred to as gendaitõ (modern swords). As of the Hatorei decree in 1876 (banning civilians from wearing swords), the need for swords declined. However, in Meiji 39 (1906) the craft gained imperial patronage.
The swordsmiths Gassan Sadakazu and Miyamoto Kanenori were appointed Tei Shitsu Gi Gei In (craftsmen by imperial appointment—equivalent to National Living Treasure). Since then, the swordsmith’s craft has continued through the Meiji (1868-1912), Taisho (1912-1926), Showa (1926-1989) and Heisei (1989-) eras until today. Today’s swordsmiths try to recreate the workmanship of eminent smiths of every period, regardless of whether they are kotõ, shintõ or shin-shintõ. In particular, recreations of tachi of the Kamakura period are a popular aim for many modern swordsmiths.
Changes in sword shape