The katana belongs to the nihontō family of swords, and is distinguished by a blade length (nagasa) of more than 2 shaku, approximately 60 cm (24 in).

[11] Pronounced [katana], the kun'yomi (Japanese reading) of the kanji 刀, originally meaning single edged blade (of any length) in Chinese, the word has been adopted as a loanword by the Portuguese.

[12] The katana is generally defined as the standard sized, moderately curved (as opposed to the older tachi featuring more curvature) Japanese sword with a blade length greater than 60.6 cm (23.86 inches) (over 2 shaku).

[13] It is characterized by its distinctive appearance: a curved, slender, single-edged blade with a circular or squared guard (tsuba) and long grip to accommodate two hands.

[15][16] However, the main weapons on the battlefield in the Sengoku period in the 16th century were yumi (bow), yari (spear), and tanegashima (gun), and katana and tachi were used only for close combat.

During this period, the tactics changed to a group battle by ashigaru (foot soldiers) mobilized in large numbers, so naginata and tachi became obsolete as weapons on the battlefield and were replaced by yari and katana.

[24] The oldest katana in existence today is called Hishizukuri uchigatana, which was forged in the Nanbokuchō period, and was dedicated to Kasuga Shrine later.

Furthermore, in the late 16th century, tanegashima (muskets) were introduced from Portugal, and Japanese swordsmiths mass-produced improved products, with ashigaru fighting with leased guns.

Due to the changes in fighting styles in these wars, the tachi and naginata became obsolete among samurai, and the katana, which was easy to carry, became the mainstream.

(The practice and martial art for drawing the sword quickly and responding to a sudden attack was called battōjutsu, which is still kept alive through the teaching of iaido.)

Lacquered saya (scabbards), ornate engraved fittings, silk handles and elegant tsuba (handguards) were popular among samurai in the Edo period, and eventually (especially when Japan was in peace time), katana became more cosmetic and ceremonial items than practical weapons.

They were both swordsmiths and metalsmiths, and were famous for carving the blade, making metal accouterments such as tsuba (handguard), remodeling from tachi to katana (suriage), and inscriptions inlaid with gold.

[42] In the late 18th century, swordsmith Suishinshi Masahide criticized that the present katana blades only emphasized decoration and had a problem with their toughness.

Their katana were often longer than 90 cm (35.43 in) in blade length, less curved, and had a big and sharp point, which was advantageous for stabbing in indoor battles.

[42] During the Meiji period, the samurai class was gradually disbanded, and the special privileges granted to them were taken away, including the right to carry swords in public.

The Haitōrei Edict in 1876 forbade the carrying of swords in public except for certain individuals, such as former samurai lords (daimyō), the military, and the police.

The craft of making swords was kept alive through the efforts of some individuals, notably Miyamoto Kanenori (宮本包則, 1830–1926) and Gassan Sadakazu (月山貞一, 1836–1918), who were appointed Imperial Household Artist.

These modern swords replicate the size and shape of the Japanese katana and are used by martial artists for iaidō and even for cutting practice (tameshigiri).

No one could win the Masamune Prize unless he made an extraordinary achievement, and in the section of tachi and katana, no one had won for 18 years before Kawauchi.

The katana's gentle curvature is attained by a process of differential hardening or differential quenching: the smith coats the blade with several layers of a wet clay slurry, which is a special concoction unique to each sword maker, but generally composed of clay, water and any or none of ash, grinding stone powder, or rust.

For a long time, Japanese people have developed a unique appreciation method in which the blade is regarded as the core of their aesthetic evaluation rather than the sword mountings decorated with luxurious lacquer or metal works.

The pattern, nie and nioi of the hamon are generally difficult to see, and the viewer usually holds the sword in his hand, changing the angle of the light as it hits the blade.

The precious swords described in this book were called "Meibutsu" (名物) and the criteria for selection were artistic elements, origins and legends.

The list of "Meibutsu" includes 59 swords made by Masamune, 34 by Awataguchi Yoshimitsu and 22 by Go Yoshihiro, and these three swordsmiths were considered special.

The katana forged by Nagasone Kotetsu, one of the top-rated swordsmith, became very popular at the time when the book was published, and many counterfeits were made.

In these books, the three swordsmiths treated specially in "Kyōhō Meibutsu Chō" and Muramasa, who was famous at that time for forging swords with high cutting ability, were not mentioned.

The reasons for this are considered to be that Yamada was afraid of challenging the authority of the shogun, that he could not use the precious sword possessed by the daimyo in the examination, and that he was considerate of the legend of Muramasa's curse.

Martial arts in which training with katana is used include aikidō, iaijutsu, battōjutsu, iaidō, kenjutsu, kendō, ninjutsu,Tenshin Shōden Katori Shintō-ryū and Shinkendo.

[77][78][79] However, for safety reasons, katana used for martial arts are usually blunt edged iaito or wooden bokken, to reduce the risk of injury.

Sharp katana are only really used during tameshigiri (blade testing), where a practitioner practices cutting a bamboo or tatami straw post.