Evolution of Katana

The introduction of iron forging technology in the Kofun Period led to the development of metal weaponry including the 直刀, first form of sword that become the base of Japanese swords to come.

Swords back then functioned not only as a weapon for battle but also as a symbolic ceremonial sword.

Swords with a luxurious exterior were only worn by authoritative figures such as those who had the right of command or cunducted rituals.

From mid to late Heian Period, swords became diverse and so did the names for them. The three main types of swords are 剣, 大刀, 横刀. They were differentiated by usage rather than the physical appearance:
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剣 was used to describe sacred swords or swords used by those of high social status

大刀 was used to describe the standard sword. This is the base for what will become the most popular shape of Japanese Katana

横刀 was used to describe swords used as a practical weapon. Originally, this term was used for swords shorter than 大刀 but the term stopped being used early into Heian.


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Another way to categorize swords was by wear.
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剣 was used for swords worn by upper class and high authority

大刀 was used for swords worn by regular people.

野太刀 was used for swords worn by soldiers going on wilderness/outdoor missions.

By the end of Heian Period, there was a system to differentiate swords by design.

(沃懸地螺鈿金装飾剣 *1)
飾剣 was ceremonial sword used by civil officers.

(金地螺鈿毛抜形太刀 *2)
毛抜形太刀 was military sword used by military officers.

Though the exact time period is debated, by the end of the Heian Period, the shape of swords drastically changed. The straight sword became curved sword for its functionality. The curve allows the blade to slice better. This curve became the standard for Japanese swords to this day.
At a similar time, the character shifted from 大刀to太刀.

The empowerment of Bushi led to a stratification within the Buke class. Bushi from a higher class Buke would carry luxurious swords to showcase their power.

兵庫鎖太刀, a popular sword between upper class Buke, was worn to intimidate others. However, by the end of Kamakura Period, this sword became a ceremonial sword.

黒漆太刀 was a sword used by the average Bushi.
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Top picture: 兵庫鎖太刀 *3
Bottom picture: 黒漆太刀 *4

Kuge, court nobles, also used swords as a identifier of social class.

Upper class kuge would carry 飾太刀.
Lower class kuge, who could not afford a 飾太刀, would carry a 細太刀.

The Mongol Invasion of Japan (*5) drastically shifted the battle style of the Japanese.
Prior to the invasion, the standard style was individual horse back duel.
After the invasion, the style shifted to a close-combat team battle. The weapon of choice became 薙刀 and 太刀 over bows and arrows.
In response to the increased demand for a strong 太刀, 太刀 became heavier and oppressive.

From around this time, it became normal for both Bushi and normal soldiers to carry two swords: a small 腰刀 along with the main 太刀.

Since the Mongol Invasion, the battle style continued to be close contact team battle. From the Sengoku Period, a shorter and lighter sword 打刀 became more popular compared to the 太刀 since the heavy 太刀 would cause fatigue and was hard to handle during battles. 太刀 from Heian and Kamakura Periods often were shaved down to become more functional.

Picture: 黒漆打刀 *6

Colorful and extravagant 太刀 started to be made.The wealthy merchant class, with the addition of new powers who emerged from the battles during Sengoku era, expressed their power and wealth through material things.
The rising popularity of Western culture within Japan, upper class Buke enjoyed wearing flashy and extravagant swords to show off their power.

One of the most significant events during Azuchi-Momoyama Period in terms of swords, is the Sword hunt(刀狩令). This sword hunt was order by Hideyoshi Toyotomi in order to maintain peace and order that was finally achieved. This rule banned farmers to own weapons, simultaneously banning farmers to become Bushi (and vice-versa).

蒔絵朱鞘大小 *7

The long standing peace led to a shift in the function of a sword from being a weapon to being a symbol.
For example, the act of wearing 2 swords became a form of showing dignity as a Bushi while being a sign of being a part the ruling class.
(Picture below: 朱溜塗大小 *8)

Since the demand for swords as a functional weapon decreased, fancy looking swords became popular. Many artistic and beautiful swords were made during this time as rich merchants would pay greatly for extravagant looking swords as a hobby.