Japanese armour first appeared in the 4th century, as evidenced by the discovery of cuirasses and basic helmets in graves.
During the Heian period (794âÂÂ1185), the unique Japanese samurai armour à Â-yoroi and dà Â-maru appeared. The Japanese cuirass evolved into the more familiar style of body armour worn by the samurai known as the dà Â, with the use of leather straps (nerigawa) and Japanese lacquerware for weatherproofing. Leather and/or iron scales were also used to construct samurai armours, with leather and eventually kumihimo (braided silk) used to connect the individual scales (kozane) of the cuirass.
The Sengoku period had created new armies of ashigaru, lightly-armoured peasant soldiers armed with long spears. Japan also began trading with European powers, principally the Portuguese Empire, which is known as the Nanban trade. Matchlock guns were sold to the Japanese in the 1500s, who rapidly improved them. These new tanegashima guns were mass-produced domestically. The combination of these two things meant samurai needed much lighter and simpler armour with different defensive qualities; this new style was called tosei-gusoku "modern armour".
When a unified Japan entered the peaceful Edo period, samurai continued to wear both plate and lamellar armour as symbols of their status.
à Âyamazumi Shrine is renowned as a repository of armour. It houses 40% of armour that the government of Japan has designated as National Treasures and Important Cultural Properties. Kasuga Grand Shrine also has a large collection of valuable armour.
Every year on Children's Day, which is May 5, households in Japan display miniature samurai armour and kabuto (elaborate helmets) as an adaptation of the former Imperial Court ritual of the tango no sekku. In feudal times, real samurai armour, kabuto, and tachi (swords) were displayed.
The earliest Japanese armour is thought to have evolved from the armour used in ancient China. Cuirasses and helmets were manufactured in Japan as early as the 4th century. Tankà  for foot soldiers, and keikà  with extra upper torso protection for cavalry, were both pre-samurai types of early cuirass constructed from iron plates connected by leather thongs.
During the Heian (794âÂÂ1185), the à Â-yoroi and dà Â-maru emerged. High-ranking mounted samurai wore the luxurious and heavily built à Â-yoroi, while the lighter dà Â-maru were typically used by lower-ranking foot soldiers. The Japanese cuirass evolved into the more familiar style known as the dà Â. Armour makers began using leather, and lacquer was applied to weatherproof the components. Leather and/or iron scales were used to construct samurai armour, with leather and kumihimo connecting the individual scales.
The artistic decoration of à Â-yoroi reached its peak around the time of the Genpei War (1180âÂÂ1185), a civil war at the end of the Heian. à Â-yoroi, which required a high degree of aesthetic refinement, might require up to of kumihimo in various colours and weaving styles to complete a single suit of armour. Toward the end of the Kamakura period (1185âÂÂ1333), even high-ranking samurai often wore the lightweight dà Â-maru.
In the Kamakura period (1185âÂÂ1333), the simplest style of armour, called , appeared. It protected only the front of the torso and the sides of the abdomen and was worn by lower-ranked soldiers. In the late Kamakura, the haramaki appeared, which extended both ends of the hara-ate to the back. During the Nanboku-chà  period (1336âÂÂ1392), ashigaru and conscripted farmers fought on foot, increasing demand for light, mobile, and inexpensive haramaki. Later, kabuto, men-yoroi (facial armor), and kote (gauntlets) were added to the haramaki, and even high-ranking samurai began to wear them.
In the Muromachi period (1336âÂÂ1573), the production process of armour became simplified, and mass production became possible at a lower cost and faster rate than before. The scales of traditional armour were connected with cords in a style called , which was so dense that the entire surface of the scales was covered with the cords. During this period, another new method, called , was adopted, in which two cords sparsely connected the scales. The technique of overlapping armour scales was also simplified. Traditional-style scales were the , in which half the scales overlapped and were connected. During this period, a new style of scales, , was developed, in which one-fourth of the scales were overlapped and connected.
In the 16th century, the Nanban trade brought matchlocks to Japan in 1543. These were called "Tanegashima" after Tanegashima, the first island the Europeans arrived on. Soon after, when Japanese smiths improved and began to mass-produce the tanegashima, warfare changed completely. The samurai needed armour that was lighter and more protective. In addition, large-scale battles also required the mass production of armour. As a result, the tosei-gusoku was created from the design of the dà Â-maru.
Additionally, the Japanese adopted a full-plate armour known as nanban dà Â-gusoku, with an iron helmet and solid cuirass, in imitation of Portuguese armour. The first set was given to Sakakibara Yasumasa by Tokugawa Ieyasu right before the Battle of Sekigahara (1600). It was handed down in the Sakakibara family. Scales were changed to , a relatively large iron or leather plate, providing better defence. Itazane could also replace a row of individual honkozane or iyozane with a single plate. This type of gusoku resembled plate armour; the front and back dà  are made from a single iron plate with a raised center and a V-shaped bottom, was called Nanban dà  gusoku (Southern barbarian gusoku). Bullet resistant armours were developed called ' ('bullet tested'), allowing samurai to continue wearing armour despite the use of firearms.
Since the armour was no longer flexible, gusoku has changed its method to facilitate donning and doffing by opening and closing the armour at a hinge. The simplified structure of the armour makes it easier to manufacture, allowing armour makers to focus on design and to increase the variety of armour appearances. For example, the iron plate was designed to resemble an old man's chest, and dà Â-maru-style gusoku was made by attaching coloured threads to its surface.
Samurai during this period, especially those with a high rank, such as daimyo, owned a lot of suits of armour. For example, Tokugawa Ieyasu owned dozens of suits, which are now owned by Kunà Âzan Tà Âshà Â-gà «, Nikkà  Tà Âshà Â-gà «, Kishà « Tà Âshà Â-gà «, Tokugawa Art Museum, The Tokugawa Museum, Tokyo National Museum, etc.
The era of warfare called the Sengoku period (1467âÂÂ1615) ended when a united Japan entered the peaceful Edo period (1603âÂÂ1868). Although samurai continued to use both plate and lamellar armour as a symbol of their status, traditional armours were no longer necessary for battle. For this reason, in the Edo period, armour in the style of the revival of the medieval period, incorporating gorgeous à Â-yoroi and dà Â-maru designs, became popular.
During the Edo period, lightweight, portable, and secret armours became popular, as personal protection remained necessary. Civil strife, duels, assassinations, and peasant revolts all required the use of armours such as the kusari (chain jacket) and armoured sleeves, as well as other types of armour that could be worn under ordinary clothing. Edo period samurai were in charge of internal security and would wear various types of kusari gusoku (chain armour) and shin and arm protection as well as armored hachimaki to protect the forehead.
Armour continued to be worn and used until the Meiji era in the 1860s, with the last use of samurai armour in 1877 during the Satsuma Rebellion.
Japanese armour was generally constructed from many small iron (tetsu) and/or leather (nerigawa) scales (kozane) and/or plates (ita-mono), connected to each other by rivets and macramé cords (odoshi) made from leather and/or braided silk, and/or chain armour (kusari). Noble families had silk cords made in specific patterns and colors of silk thread. Many of these cords were constructed of well over 100 strands of silk. Making these special silk cords could take many months of steady work, just to complete enough for one suit of armour.
These armour plates were usually attached to a cloth or leather backing. Japanese armour was designed to be as lightweight as possible as the samurai had many tasks including riding a horse and archery in addition to swordsmanship. The armour was usually brightly lacquered to protect against the harsh Japanese climate. Chain armour (kusari) was also used to construct individual armour pieces and full suits of kusari were even used.
A full suit of traditional Samurai armour could include the following items:
, are samurai armours with a lamellar cuirass constructed from individual scales , old fashioned armours used before the introduction of firearms in Japanese warfare (pre-Sengoku styles).
the so-called "modern armours" made from iron plates (ita-mono) instead of individual scales (kozane). Tosei-gusoku became prominent starting in the 1500s due to the advent of fire arms, new fighting tactics and the need for additional protection.
At present, by the Law for the Protection of Cultural Properties, important armors of high historical value are designated as Important Cultural Properties (Jà «yà  Bunkazai, éÂÂè¦ÂæÂÂÃ¥ÂÂ財), and special armors among them are designated as National Treasures (Kokuhà Â, å½å®Â). The armors designated as cultural properties based on the law of 1930, which was already abolished, have the rank next to Important Cultural Properties as Important Art Object (Jà «yà  Bijutsuhin, éÂÂè¦Âç¾Âè¡ÂÃ¥ÂÂ).
The Association for the Research and Preservation of Japanese Helmets and Armor (, Nihon Katchu Bugu Kenkyu Hozon Kai), a general incorporated association, rates high-value armors in five grades. In order of rank, they are, from highest to lowest, Juyo Bunka Shiryo (éÂÂè¦ÂæÂÂÃ¥ÂÂè³ÂæÂÂ, Important cultural article), Koshu Tokubetsu Kicho Shiryo (ç²種ç¹å¥貴éÂÂè³ÂæÂÂ, Especially precious article first grade), Tokubetsu Kicho Shiryo (ç¹å¥貴éÂÂè³ÂæÂÂ, Especially precious article.), Kicho Shiryo (è²´éÂÂè³ÂæÂÂ, Precious article), Hozon Shiryo (ä¿ÂÃ¥ÂÂè³ÂæÂÂ, Article worth preserving).