Where a katana's signature sits reveals which way up it was worn
Japanese smiths carved their signature on the side of the tang that faced outward when worn. Because the older tachi hung edge-down and the katana was thrust through the sash edge-up, the signature's position usually tells the two apart, and signatures switching sides around 1400 show samurai changing how they carried swords.
The word katana, meaning one-sided blade, appears in Japanese as early as the Nihon Shoki of 720, in contrast to the double-edged tsurugi. Today it denotes a moderately curved, single-edged sword with a blade longer than 2 shaku, about 60.6 centimetres, a round or squared guard and a grip long enough for two hands. In Japan the precise term is uchigatana, the striking sword. Portuguese borrowed the word as catana, meaning a large knife or machete.
The katana grew out of the sasuga, a short blade carried as a backup by low-ranking foot soldiers of the Kamakura period, whose main weapon was the long naginata. As very long swords became fashionable in the Nanboku-chō period, these side arms were gradually lengthened. The oldest surviving example, the Hishizukuri uchigatana, dates from that era and was later offered to Kasuga Shrine. From the Muromachi period, many old tachi were cut down at the base and converted into katana.
Battlefield change drove its rise. The Ōnin War of the late 15th century mobilised masses of hired farmers, the ashigaru, who fought on foot with katana shorter than tachi. In the Sengoku period, bows, spears and muskets, introduced from Portugal, dominated, while swords served for close fighting. Tachi and naginata fell out of use, and the handy katana became standard, while tachi turned into status symbols for senior samurai.
Carried edge-up, the katana could be drawn and swung in a single motion, the basis of quick-draw swordsmanship still taught as iaido. Its reputation spread early: in 1430, a Korean swordsmith who had learned Japanese techniques presented his king with a blade judged equal to Japanese work. Katana also served as gifts between lords and samurai and as offerings at Shinto shrines.
Source: Katana
