Swords first appeared in Japan in 240 – 280 AD when China sent two double-edged tsurugi swords as gifts to Queen Himeko. It is unknown for sure, but it is generally believed the art of forging steel into swords spread from China to Japan sometime during the third and fourth centuries. Straight, single-edged swords called chokuto have been found dating to the fifth century. More advanced hardening methods during the forging process developed during the sixth century.
Around the eight century swords became curved to help accommodate fighting on horseback. These early swords were called tachi, and were characterized by a long, curved, single-edged blade. Two common types of tachi during this period were the kogarasumaru and kenukigatatachi. The tachi reigned supreme as the weapon of choice in Japan from the eighth to twelfth century. During this time the practice of using soft steel for the inner core and harder steel for the outer surface and blade became common. It became customary for the sword smith to sign the blade. The oldest blade with a sword smith's signature is by Sanjo Munechika.
During the thirteenth century samurai used tachi and other weapons to fight off invading Mongols. During these invasions it became apparent the tip of the tachi was too easily broken and difficult, if not impossible, to repair. Designs of later swords would be influenced by this fact. During the fourteenth century longer swords, around 120-150cm, were created. The long swords were good for delivering devastating blows, but they were not quick to draw. In the fifteenth century swords were shortened to around 70cm to accommodate quicker draw times. These swords were called uchigatana.
During the sixteenth century swords became even shorter, averaging 60-65cm, to facilitate increased portability. These swords are called katana, and were carried with the blade facing upward so that a deadly strike could be carried out while drawing the sword. In contrast, the katana's predecessor, the tachi, was carried with the blade facing downward. During this period the use of katana was at its height in Japan as firearms had not been introduced to Japan yet.
When the Portuguese brought firearms to Japan in 1543 Japanese warlords knew the strategy of warfare would be dramatically altered. Standing armies were trained and equipped with muzzle-loading firearms. Although firearms were more effective in battle, samurai still carried their daisho, a long and a short sword, as a sign of their class. This custom ended in 1868 when Emperor Meiji outlawed the right of samurai to carry weapons. A further blow to samurai swords came when they were made illegal during the occupation of the Allied forces after World War II. Today many swords classified as national treasures are still missing.