stylistic:tone
Kotō (Old swords)

Katana originates from sasuga (刺刀), a kind of tantō (short sword or knife) used by lower-ranking samurai who fought on foot in the Kamakura period (1185–1333). Their main weapon was a long naginata and sasuga was a spare weapon. In the Nanboku-chō period (1336–1392) which corresponds to the early Muromachi period (1336–1573), long weapons such as ōdachi were popular, and along with this, sasuga lengthened and finally became katana. Also, there is a theory that koshigatana (腰刀), a kind of tantō which was equipped by high ranking samurai together with tachi, developed to katana through the same historical background as sasuga, and it is possible that both developed to katana. The oldest katana in existence today is called Hishizukuri uchigatana, which was forged in the Nanbokuchō period, and was dedicated to Kasuga Shrine later.

The first use of katana as a word to describe a long sword that was different from a tachi, occurs as early as the Kamakura period. These references to " uchigatana " and " tsubagatana " seem to indicate a different style of sword, possibly a less costly sword for lower-ranking warriors. Starting around the year 1400, long swords signed with the katana- style mei were made. This was in response to samurai wearing their tachi in what is now called " katana style" (cutting edge up). Japanese swords are traditionally worn with the mei facing away from the wearer. When a tachi was worn in the style of a katana, with the cutting edge up, the tachi 's signature would be facing the wrong way. The fact that swordsmiths started signing swords with a katana signature shows that some samurai of that time period had started wearing their swords in a different manner.

By the 15th century, Japanese swords, including katana, had already gained international fame by being exported to China and Korea. For example, Korea learned how to make Japanese swords by sending swordsmiths to Japan and inviting Japanese swordsmiths to Korea. According to the record of June 1, 1430 in the Veritable Records of the Joseon Dynasty, a Korean swordsmith who went to Japan and mastered the method of making Japanese swords presented a Japanese sword to the King of Korea and was rewarded for the excellent work which was no different from the swords made by the Japanese.

Traditionally, yumi (bows) were the main weapon of war in Japan, and tachi and naginata were used only for close combat. The Ōnin War in the late 15th century in the Muromachi period expanded into a large-scale domestic war, in which employed farmers called ashigaru were mobilized in large numbers. They fought on foot using katana shorter than tachi. In the Sengoku period (period of warring states) in the late Muromachi period, the war became bigger and ashigaru fought in a close formation using yari (spears) lent to them. 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. On the battlefield in Japan, guns and spears became main weapons in addition to bows. 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 dazzling looking tachi gradually became a symbol of the authority of high-ranking samurai.

On the other hand, kenjutsu (swordsmanship) that makes use of the characteristics of katana was invented. The quicker draw of the sword was well suited to combat where victory depended heavily on short response times. (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.) The katana further facilitated this by being worn thrust through a belt-like sash (obi) with the sharpened edge facing up. Ideally, samurai could draw the sword and strike the enemy in a single motion. Previously, the curved tachi had been worn with the edge of the blade facing down and suspended from a belt.

From the 15th century, low-quality swords were mass-produced under the influence of the large-scale war. These swords, along with spears, were lent to recruited farmers called ashigaru and swords were exported. Such mass-produced swords are called kazuuchimono, and swordsmiths of the Bisen school and Mino school produced them by division of labor. The export of katana and tachi reached its peak during this period, from the late 15th century to early 16th century when at least 200,000 swords were shipped to Ming dynasty China in official trade in an attempt to soak up the production of Japanese weapons and make it harder for pirates in the area to arm. In the Ming dynasty of China, Japanese swords and their tactics were studied to repel pirates, and wodao and miaodao were developed based on Japanese swords.

From this period, the tang (nakago) of many old tachi were cut and shortened into katana. This kind of remake is called suriage (磨上げ). For example, many of the tachi that Masamune forged during the Kamakura period were converted into katana, so his only existing works are katana and tantō.

From around the 16th century, many Japanese swords were exported to Thailand, where katana-style swords were made and prized for battle and art work, and some of them are in the collections of the Thai royal family.

From the late Muromachi period (Sengoku period) to the early Edo period, samurai were sometimes equipped with a katana blade pointing downwards like a tachi. This style of sword is called handachi, "half tachi ". In handachi, both styles were often mixed, for example, fastening to the obi was katana style, but metalworking of the scabbard was tachi style.

In the Muromachi period, especially the Sengoku period, people such as farmers, townspeople, and monks could have a sword. However, in 1588 Toyotomi Hideyoshi banned farmers from owning weapons and conducted a sword hunt to forcibly remove swords from anyone identifying as a farmer.

The length of the katana blade varied considerably during the course of its history. In the late 14th and early 15th centuries, katana blades tended to have lengths between 70 and 73 centimetres (28 and 29 in). During the early 16th century, the average length dropped about 10 centimetres (3.9 in), approaching closer to 60 centimetres (24 in). By the late 16th century, the average length had increased again by about 13 centimetres (5.1 in), returning to approximately 73 centimetres (29 in).