When exploring the prototype of the Japanese sword, we must trace our attention back to the Nara period in Japan around the 8th century AD. During this period, through cultural exchange channels such as envoys to Tang China, the sword-making techniques of the Tang Dynasty in China, especially the forging process of the popular “Tang Broadsword” at that time, were systematically introduced to Japan. These swords and knives from the Chinese mainland usually have relatively straight blades, with lengths mostly ranging from 70 to 90 centimeters. Their core forging techniques, such as the steel coating method, provided crucial technical blueprints for Japanese artisans. An 8th-century “Gold and Silver inlaid Shotang Great Sword” in the collection of the Shosoin, with a blade length of approximately 62 centimeters, is a precious physical example of imported or imitated swords in the style of the Chinese mainland during this period. It can be regarded as the initial object for Japanese local swordsmiths to learn from and imitate, namely the earliest prototype for katana.
Japanese swordsmiths did not stop at simple imitation. They carried out technological iterations for several centuries in response to Japan’s unique combat methods (mainly one-handed chopping on horseback) and the characteristics of iron ore resources. A key innovation is the mature application of the “pick-made” blade structure (i.e., the arched structure with edges), which significantly enhances the structural strength and bending resistance of the blade. Another revolutionary advancement is the refinement of the “folding forging” process. Craftsmen repeatedly fold and forge jade steel and sheet steel with different carbon contents in a complex way of more than 15 layers. This process may involve up to tens of thousands of hammering, aiming to extract impurities from the steel and precisely control the carbon content within the optimal range of 0.6% to 0.7%. Thus, at the microscopic level, a perfect balance is achieved between the extremely high hardness of the blade (up to HRC60 or above) and the toughness of the blade body.
Social demand is another core driving force for the evolution of samurai sword prototypes. From the middle of the Heian period (around the 10th century), a unique samurai class rose in Japan, and cavalry warfare became mainstream. Compared with the straight sword, the “katana” with its elegant curvature is more suitable for one-handed slaying on horseback. Its curvature (reverse) is usually between 1.5 and 2.5 centimeters. The way the blade faces down when worn also makes it convenient to draw the sword immediately. By the Kamakura period (the end of the 12th century), the requirements for actual combat had further increased, giving rise to the “katana”, which was stronger and more suitable for infantry combat. The way it was worn was changed to have the blade facing upwards, facilitating quick drawing of the sword to confront the enemy. This directly laid the foundation for the basic form of the later Katana. The large-scale conflicts such as the Genpei Battle in 1185 were like a huge practical test ground, accelerating the survival of the fittest among various sword equipment prototypes in a harsh environment.
Ultimately, through hundreds of years of technological accumulation and practical feedback, the classic form of katana stabilized around the Muromachi period of the 14th century. Its typical specifications include: the blade length (from the starting point to the pickaxe) is approximately 70 cm, the curvature (reverse) is about 1.8 cm, and it adopts a unique “shot cage” knife stem design to enhance strength. Every famous sword, such as the legendary “Demon Sword Muramasa” or “Ichigo Ichigo”, has been born without a profound understanding of the early technological prototypes on the Chinese mainland, an extreme exploration of local materials science, and a precise grasp of its practicality on the battlefield. This process from introduction, digestion, re-innovation to finalization not only created a legendary weapon, but also demonstrated the outstanding ability of Japanese craftsmanship to localize foreign technologies and bring them to perfection.