Yari (槍) is the Japanese term for spear, or more specifically, the straight-headed spear. The martial art of wielding the yari is called sōjutsu. Yari measured anywhere from one meter to upwards of six meters (3.3 to 20 feet). The longer versions were called ōmi no yari while shorter ones were known as mochi yari or tae yari. The longest versions were carried by foot troops (ashigaru), while the samurai usually carried the shorter versions.
Yari were characterized by a straight blade that could be anywhere from several centimeters long, to 3 feet (0.9 meters) or more. The blades were made of the same high-quality steel that the swords and arrow-heads of samurai weapons were forged with, and yari blades were very durable. Over history many variations of the straight yari blade were produced, often with protrusion on a central blade. Yari blades (points) had extremely long tangs which were usually longer than the sharpened portion of the blade. The tang protruded into a hollow portion of the handle. This resulted in a very stiff shaft and made it nearly impossible for the blade to fall or break off.
The shaft (nakae) came in many different lengths, widths and shapes; made of hardwood and covered in lacquered bamboo strips, these came in oval, round, or polygonal cross section. These in turn were often wrapped in metal rings or wire, and affixed with a metal pommel (ishizuki) on the butt end. The yari could be considered a much higher quality weapon than the average spear due to these unique attributes. Yari handles were often decorated with inlays of metal or semiprecious materials such as brass pins, lacquer, or flakes of pearl.
A sheath for the blade called saya was also part of a complete yari.
Various types of yari points or blades existed. The most common blade was a straight, flat, design that resembles a straight-bladed double edged dagger. This type of blade could cut as well as stab and was sharpened like a razor edge. Though yari is a catchall for spear, it is usually distinguished between kama yari, which have additional horizontal blades, and simple su yari (choku-sō) or straight spears. Yari can also be distinguished by the types of blade cross section: the triangular sections were called sankaku yari and the diamond sections were called ryō-shinogi yari.
The fukuro yari (袋槍, bag spear or socket spear) sported a more European style fitting of the straight head. Instead of the yari's traditional very long embedded tang, an entirely metal socket which slipped over the narrowed end of the pole, The unit was forged as a single piece of both socket and blade. This design was rare next to the traditional 'long-tang' configuration.
A kuda yari (管槍, tube spear) was not very different in construction than another simple choku yari. However for this spear, the upper hand gripped a hollow metal tube that allowed the yari to "screw" while being thrust. This style of sojutsu is typified in the school Owari Kan Ryū.
Kikuchi yari (菊池槍, spear of Kikuchi) were one of the rarest designs, possessing only a single edge. This created a weapon that could be used for hacking and almost resembled a straight edged naginata.
Yajiri nari yari (鏃形槍, spade-shaped spear) had a very broad "spade-shaped" head. It often had a pair of holes centering the two ovoid halves.
Magari yari (曲槍, curved spear), also called jūmonji yari (十文字槍, cross-shaped spear), looked something similar to a trident or partisan and brandished a pair of curved blades around its central lance. Occasionally called maga yari in modern weaponry texts. In the Koei video game Samurai Warriors, Sanada Yukimura uses one such weapon.
The kama yari (鎌槍, sickle spear) gets its name from a peasant weapon called kama (lit. sickle or scythe). However, a kama isn't a scythe as most Westerners think of it, a giant, curved blade connected at right angles to a two-meter-long wooden handle, but rather a much smaller version, with a less dramatically curved blade and a straight wooden handle approximately two feet long.
The kata kama yari (片鎌槍, single-sided sickle spear) had a radical weapon design sporting a blade that was two-pronged. Instead of being constructed like a military fork, a straight blade (as in su yari) was intersected just below its midsection by a perpendicular blade. This blade was slightly shorter than the primary, had curved tips making a parallelogram, and was set off center so that only 1/6th of its length extended on the other side. This formed a kind of messy 'L' shape.
The tsuki nari yari (月形槍, moon-shaped spear) barely looked like a 'spear' at all. A polearm that had a crescent blade for a head, this could be used for slashing and hooking.
A kagi yari (鉤槍, hook spear) had a long blade with a side hook much like that found on a fauchard. This could be used to catch another weapon, or even dismount a rider on horseback.
Bishamon yari possessed some of the most ornate designs for any spear. Running parallel to the long central blade were two 'crescent moon' shaped blades facing outwards. They were attached in two locations by short cross bars, making the head look somewhat like a fleur-de-lis.
Yari are believed to have been derived from Chinese spears, and while they were present in early Japan's history they did not become popular until the 13th century. The original warfare of the bushi was not a thing for 'commoners'; it was a ritualized combat usually between two warriors who would challenge each other via horseback archery and sword duels. However the invasions of Mongols in 1274 and 1281 changed Japanese warfare and weaponry. The Mongol-employed Chinese and Korean footmen wielded long pikes, fought in tight formation, and moved in large units to stave off cavalry. Polearms (including naginata and yari) were of much greater military use than swords, due to their much greater range, their lesser weight per unit length (though overall a polearm would be fairly hefty), and their great piercing ability. Swords in a full battle situation were therefore relegated to emergency sidearm status from the Heian through the Muromachi periods. Yari overtook the popularity of the daikyū for the samurai, and foot troops (ashigaru) used them extensively as well. But by the Edo period the yari had fallen into disuse: with the greater emphasis on small-scale close quarters combat and the convenience of swords (as opposed to long battlefield weapons), polearms and archery lost their practical value. During the peaceful Edo era, yari were still produced, sometimes even by good swordsmiths. They existed as a ceremonial weapon for most of this era.