One of the most famous and deadliest ancient weapons in Japan is the Japanese Sword-Katana.
Katana (刀) is the most well known of the traditionally made Japanese swords. In the feudal period of Japan, Samurais used to wear them as a protection as well as status symbol. The katana is characterized by its distinctive appearance. A curved, single-edged blade with a circular or squared guard and long grip to accommodate two hands.

The roots of Katana reach back all the way into the 13th century. Previous swords were unable to cut through the boiled leather armor of the Mongols during the Mongol invasion of Japan, which led to a change in the designs of Japanese swords. The katana was often paired with a similar smaller companion sword or dagger.
The Kamakura (1192 to 1336) and Muromachi (1337 to 1573) periods were without a doubt the Golden Age of Samurai sword history. During these periods, there were many invasions in Japan. As a result, there was need for an effective sword to fend off invaders successfully. Consequently, during the Muromachi period, smiths developed the curved katana sword which was more functional during horseback fighting. Furthermore, some of the most beautiful swords of the history of katana arose in this period.

However, after the Muromachi period, there were fewer wars and invasions in Japan. This reduced the demand for katana swords. More superior weapons like the gun were also introduced forcing the sword smiths to abandon their craft. This had a negative effect on sword craftsmanship because the skills of the earlier smiths were not passed to new generations. The katana sword rose to popularity again when the great emperor Shogun Hideyoshi allowed the privileged Samurai class to carry the katana.

1876 marked the start of civilization in the country and Japanese warriors and citizens were ordered to stop carrying swords. This dark period forced the few remaining smiths to close their businesses. The Japanese army then abandoned the use of Samurai swords and adapted modern weapons from the West.

Katanas are traditionally made from a specialized Japanese steel called tamahagane (玉鋼) which is created from a traditional smelting process that results in several, layered steels with different carbon concentrations. The gentle curvature of a katana is reached by a process of differential hardening. After the blade is forged, it is then sent to be polished. The polishing takes between one and three weeks. The polisher uses finer and finer grains of polishing stones in a process called glazing, until the blade has a mirror finish.

The Katana gained a lot of popularity and fascination in the western world through several samurai movies, videogames as well as western movies such as Kill Bill, Matrix or Suicide Squad. While the Katana is no longer used for military purposes, in temporary Japan it continues carrying ceremonial and historical importance in Japanese culture as a fine piece of art. Modern martial artists still use a variety of katana. The most famous martial arts using katana now are Kenjutsu (剣術), Iaido (居合道) and Kendo (剣道).