Why didn't Japanese infantrymen and samurai use shields?

well first of all samurai used two hands to weld a katana cant hold a shield at the same time. the second thing is they were not cowards to hide behind shields they were straight up fighters.

The reason is most likely very simple, as stated before shields are primerily an arrow defense. But in order to make a good shield you need raw hide and glue, two things the Japanese didn't have much of.

From what I gather, evolution on the way of war runs slightly parallel with that of the native American Indians, mainly the Iroquous (vaguely) since both use mobility as the primary stratagem by geographical regions, neighbouring tribes/clans, weapon technology, principals etc. Native Americans would be best example so, mainly mobility would suit raid, ambushes etc, the Iroquos had a lot of forest, better for ambushes and so shields would useful still since they fought a lot in hand to hand combat, but overall, just not worth it as it interferes with the primary way of war.

Mobility, this basic concept in itself is a root for which all the factors go in like, shields hitting tree branches, materials, way of thinking etc. The samurai developed armor which has the primary function of a shield but also does not interfere with their weaponry technology/military thinking/military requirements, realizing just now that their are, countless reason why not to use a shield in war and why they didn't.

Last big example is as with the Europeans introducing gunpowder to the Native Americans, even if they decided to use shields in war, it would be irrelevant. Or the Japanese emperor forbids the use of shields, or that shields promote defensive temperaments, or maybe to block without skill, is the way of the coward and not a true warrior, not worthy.

And finally, perhaps it's the influence of the Greeks and lack of that, like the lemmings - where one goes they all go.

We may read what Whitaker has related in his "A Complete System of Universal History" (1821) about Jedso (Hokkaido):

Their weapons are bows, arrows, and lances, and a kind of short scymetar. On some occasions they use poisoned arrows, being choleric, quarrelsome, and revengefull. Instead of shield or cuirass, they wear coats made of small, thin laths.

Charlotte Salway, a famous sinologist, wrote:

The mighty sword and arrows were the chief defensive weapons. These they made in endless forms and fashions to suit all requirements—for distant practice or hand-to-hand fighting. Generals carried flat and closed fans, for giving direction on the battle-field or for use as a shield at close quarters.

In general, there were several factors which discourage the use of shields. Firstly, metal was relatively more expensive in Japan than medieval Europe. Therefore, what metal they had tended to be worked to higher quality and used in offensive weapons. It would have been seen as wasteful to the Japanese to use metal on a shield, since it could be made into something much more valuable: a weapon.

A second factor derives from the first. Since the Japanese lavished more attention on their steel it tended to be higher quality. Good quality steel can cut through any typical shield. A shield that could withstand a well made sword would be very heavy and expensive, completely ineconomical. Early knights used shields because they often fought peasants who used clubs and rocks.

The third factor is philosophical. Japan from 1608 was in the great peace of the Shogunate, so practical war technology was secondary to politics and etiquette. This led to a sword-centered philosophy. Salway writes:

Arms were in great request during the turbulent times, when the Minamoto and Taira clans contended for the right of governing the people in a military sense; but when Ieyasu settled the long dispute and restored tranquillity, the beautifying of swords and sword furniture became a matter of great interest to all privileged to carry these protective weapons. In the sword was centred all the pride of the wearer; it became his dearest friend, the guardian of his honour as well as his greatest treasure.... Upon the sword, as upon everything else which these Orientals produce, labour was abundantly lavished; every portion received minute attention—-the guard, the blade, the hilt, the scabbard, down to the smallest accessories. Not only was it an appendage of dress in the daytime, but it was carefully laid aside in a suitable resting-place at night; and in the living-room of every house was seen a raised dais, with a stand specially provided for the purpose of holding the sword.

A samurai would have considered use of a shield, even when facing arrows or stones, as a dishonor because it would seem cowardly or self-serving; in other words a shield is inconsistent with the principles of bushido.

Also, just to make the point concerning the quality of Japanese steel, even today it is the best. For example, the best shears in the world are all from Japan. Here is an example from Naruto, one of the better makers:

That's right, $2000 for a pair of scissors. And yes, they cut through medieval European shields like butter.

Dorothy Perkins's book, The Samurai of Japan: A Chronology from their Origin in the Heian Era to the Modern Era, foot soldiers in eastern Japan were equipped with shields and long spears during the sixth century AD. called "Tate" they infact did use shields. However By the 1600's a new weapon was deployed; firearms and shields that were flat panel and angled manifested so infantrymen could fire behind. Largely since Samurai Were also well trained in the use of polearms and bow/arrow; you can't use said weapons without BOTH hands, as such hand-held shields became impractical so they instead incorporated those onto their armor. Large armor plates were attached to the shoulders to provide the protection in place of a personal shield. You can see pictures of samurai armor, Unlike European armor which the shoulder tapers and curves to the arm, samurai armor has huge plates on the shoulders that along with their helmets, act like gutters for precipitation and downward facing projectiles.

Another aspect is, the culture of warfare between Japan and Europe was different. In the West, armor was evolving toward full and total protection and the result was the plate armor. Weapons developed in parallel, seeking to pierce or crush those plates rather than cut in. Japan never had that problem; so heavy weapons like halberds, Maces and war hammers never manifested, thus the need for shields faded into irrelevance.

Armor basically does the same job as a shield, and Japanese armor is extremely advanced even without the use of metals, plus the Ashigaru were most of the time given the long spear like the pike but minor differences. I forget the name but anyway, or the bow, some were bands of raiders that used swords, taken from fallen foes, and like the samurai following suit, no shield.

I would just sum it up to it's a different world, just like the feeling when you are exposed to another culture or area, country basically, as much as you may have read and learned from it, once you experience it, it's another world because it just is unique.

Pole arms/spears were the favored weapon on a true battlefield for 95% of cultures. Knight, samurai, Greeks, etc. The Romans are a bit of an exception in that the pilim wasn't their primary. But a soldier would still own a pole arm.

A sword is more like a pistol. A reliable side arm for close quarters or if your primary weapon breaks (or jams.) but when a man with a rifle meets a man with a pistol, the man with the pistol is a dead man. Just aim for the heart.

Swords were also used in Japanese duels as a ceremonial weapon. Another reason to use a sword is because theres a risk of getting into a fight and you want to be prepared but you aren't for sure entering a battle and can't carry a spear all day.

Given there is an accepted answer, and (I believe) there remains some misconception in answers provided here, I hope to clarify a few points about the usage of defensive shields in Japanese warfare and other related matters. Also, to help Kentaro Tomono (who seem to be particularly interested).

Before going through a list of misconceptions (below), the main one to consider is this, in OP's question:

... shield use was obsolete by the Edo period because they were clumsy, and because Japan lacked Hellenistic influences.

It should be noted OP goes on to doubt the validity of this assertion.

Answer: Instead of seeing hand-held shields as inconvenient during the Edo period, or any other militaristic considerations, the real answer lies in the fact that from the Edo period onwards (1600's), there was a significantly reduced role for samurai as warriors. In other words, if the shield was not used during Edo period, it was simply because samurai caste as warriors did not really exist anymore simply due to less battles.

During the feudal period, samurai were warriors that fought for a lord in a feudal relationship. The Edo period, however, was largely free from both external threats and internal conflicts. Instead, the samurai maintained their fighting skills more as an art than to fight. Samurai were paid a stipend from their lord, limiting their ties to the economic base. In addition, samurai could not own land, which would have given them income independent from their duty.

Source: Wikipedia on Edo society (emphasis mine).

In historical discussions, generally, the concept of the samurai as warriors is different from the Edo period (1603–1868 CE) onwards. In other words, prior to the Edo period/Togukawa shogunate, Samurai were warriors. But they are less frequently considered as such from Edo period onwards.

The caste of Samurai as warriors, although identified early during 8th century (Nara period), only came into their own during late Heian, i.e. late-12th century. The Heiji Rebellion of 1160 was a turning point (in establishing this warrior class). By the time we get to the Tokugawa (Edo) period, over 400 years later, the samurai had evolved into more bureaucrats (albeit highly educated), than warriors.

On fighting skills as art, this is the concept of bushido, which was established during the Edo period, not before. So, instead of seeing it as stand-alone chivalric code, it was created in an environment (late-16th century) with specific emphasis on developing oneself to be a learned-warrior or warrior-monk. Another way of stating this, the "bun" (文) and "bu" (武), literary study and military arts, respectively.

Other points to consider:

1. Lamellar Armour - Equating hand-held shields with the only form of defence. The unique Samurai armour (coupled with the preference by East Asian warriors' for lamellar type) had a significant role in defence. (This applies to horse-based Samurai only.)
2. The Japanese stirrup, contrary to accepted answer, has been in use since 4th/5th century because of Xianbei warriors, in particular the Tuoba Wei (拓跋魏).
3. A Samurai's cloak (horo) was also defensive, though not often appreciated.

By the way, not all Samurai could use horses, only the upper-class Samurai were permitted to do so. Henceforth, we are referring to the upper-class when we use the term "Samurai".

1. Lamellar Armour

From question title:

Why didn't Japanese infantrymen and samurai use shields?

Answer: As OP & others have stated, infantry archers did use shield walls to protect themselves. In European context, it would be mantlets.

In the context of horse-riding Samurai, we actually mean "hand-held shields", which are smaller/lighter than standard infantry shields.

Answer: In the context of lamellar armour, the unique design of Samurai armour, which was different to European knights, precluded the need for hand-held shields, although they did use them on occasion (especially against gunpowder weapons in later medieval period, tameshi gusoku /"bullet tested").

Although the preference is not to use hand-held shields, sometimes the Samurai class did use shields whilst riding into battle.

On why didn't the Samurai use shields as often, in addition to the inconvenience a hand-held shield poses to a horse-borne archer, one of the clearest reason is because the unique Samurai armour, the kogusoku and ōsode. Used well together, the design of the Samurai armour allowed for better movement, less restrictions (the kogusoku). In particular, the lamellar plates (ōsode), were usually sufficiently strong defensively.

Japanese warriors never, on the other hand, appear to have developed much interest in hand-held shields, probably because of the incompatibility of this sort of armament with mounted archery. There are, in fact, only two appearances of hand-held shields in early medieval sources, both in thirteenth-century picture scrolls. One depicts a lightly armored foot soldier wielding a sword in his right hand and a rectangular wooden shield about 60 cm by 40 cm in his left, as he participates in an attack on a warrior’s home. The other shows a warrior on horseback carrying what appears to be an ordinary, free-standing shield.

In lieu of hand-held shields, bushi adopted heavy body armor specifically devised for fighting with bow and arrow from horseback. ... In some earlier Japanese lamellar armors, the parts protecting the wearer’s shoulders, neck and torso were made all of one piece. But this design restricted shoulder and arm movement, hindering easy use of the bow and arrow. To maximize freedom of motion for archers, the cuirass of the ōyoroi was cut away around the shoulders and armpits, and the resulting gaps were covered by free-hanging accessory pieces (collectively called kogusoku).

Large, flat, rectangular plates of lamellae, called ōsode, which were easily the most recognizable feature of early medieval armors, afforded protection for the shoulders and upper arms. About 30 cm square, ōsode served mounted archers (who needed both hands to ride and shoot) as substitutes for hand shields.

Source: Friday, K.F. Samurai, Warfare and the State in Early Medieval Japan, Routledge, 2004, pp.90-3. More information on the Japanese ōsode is available here.

Actually, there is another potential reason for lower frequency of shield use by Japanese samurai. I am going to turn OP's question around, were European knights considered horse-archers? If not (some do not accept this), then it explains why medieval European knights did use hand-held shields more frequently.

2. Abumi - the Japanese stirrup

Image Source: Wikipedia

It is wrong to say: "... stirrups were not developed in Japan forcing the samurai to hold reins or grip onto the saddle with their knees whilst using a bow" (answer by Hux).

Referring to the Edo period, 17th century Japan, the Japanese stirrup has been in use more than a 1000 years earlier, i.e. 5th century (Wikipedia). It could even be a century earlier, 4th century, because of influence from heavy cavalry of Xianbei Toba / Tuoba Wei (拓跋魏) and the fact that Japanese samurai armour has been dated to 4th century.

However, The Cambridge World History, Volume 4, (2015), states categorically the influence of Tuoba Wei (拓跋魏), via Goguryeo, reached Japan in 5th century (p. 421 - emphasis mine):

During the fourth and early fifth centuries, Xianbei bands in the north-east (of China) established a series of dynasties in the area of southwestern Manchuria and northeastern China proper. The presence of Xianbei empires in this area had the effect of permanently sundering the Korean Peninsula from Chinese administration. Xianbei dynasties interacted dynamically both with Chinese culture and with the proto-Korean kingdom of Koguryo to their east. Koguryo, for example, may have learned the technique of cavalry warfare from the Xianbei. Koguryo-style cavalry armor then passed down to the southern tip of the Korean Peninsula, and across to the Japanese islands by the fifth century (where mounted archery would eventually become the characteristic combat style of later Japanese samurai).

3. The Samurai's Cloak (Horo)

In addition to Wikipedia, this is from Handbook To Life In Medieval And Early Modern Japan (2006), p. 172 (emphasis mine):

Another means of defense was a length of fabric draped over the back of a warrior’s armor that could catch stray arrows, especially in a charge or other rapid maneuver that caused the cape to billow. Later this device, known as a horo, took the form of a large sack that inflated when the warrior moved, thus harnessing the force of the trapped air to repel arrows. Sometimes, this cloaklike bag positioned on the back of the armor was stiffened with a cage of reeds to ensure that few arrows would meet their target. Further, this fabric horo served as one means of protection for a messenger, as they possessed little other means of defense and often traveled rapidly and without accompanying troops. When a lord’s seal (mon) was added to the cloak, the messenger could be easily identified whether approaching or retreating.

Additional info on Horo (a samurai's cloak)

• a short video explaining how it works, 2:55 onwards - https://youtu.be/nb1WcI9TNXw
• also had a ceremonial function, in that it was used to wrap up the decapitated head of a defeated samurai as a mark of respect. This is according to Hosokawa Yusai (who served both Toyotomi Hideyoshi and Tokugawa Ieyasu), in his Collection of General Principles 1671.
• I don't remember the source anymore, but a horo could also be very important for signalling - if it was won by a daimyo or a samurai leading a battle (i.e. more than a messenger), such as Shoni Kagesuke who fought the Mongols. In the press of battle, a horo would allow fellow warriors to quickly locate their leader and his directions for the on-going battle. (The link mentions the role of Shoni Kagesuke in Mongol's invasion of Japan, of 1274 & 1281, but not about how he used his horo).

It is important that a shield is primarily a defence against missile fire, and only secondarily a defence against melee weapons. As noted here (page 107) the quality of Japanese armour, combined with the failure to utilize crossbows and the relative weakness of their strung bows, meant that a samurai was well protected against missile fire by his armour:

Japanese bushi confronted very different technological as well as geographical and organizational circumstances. To begin with, they were forced to make do with bows distinctly inferior to those available on the continent. The kiyune and fusetake-yumi of the tenth to twelfth centuries were particularly weak and, used in conjunction with the heavy oyoiroi armors favoured by early medieval samurai, forced warriors to shoot only at very close range - usually less than 10 metres - and to target with precision the gaps and weak points in the armour of specific opponents.

Wow, where to start.

Basically, ignore anything in the previous answer regarding Europe and shields.

As far European metallurgy goes, pattern welding was in use as early as the 2nd and 3rd centuries. The technique continued to be used up until about the end of the viking era (mid 11th century) when quenching and tempering basically took over.

As a general rule, shields got smaller as armour got better and became more common. Far from being a secondary defence in melee, shields are not clumsy and are excellent for both attack and defense. As I said, they fell out of use in Europe because improvements in body armour made them superfluous. NOT because your off-hand can be put to better use. Unless you are extremely well trained, using two swords is simply an invitation for a humiliating death. I think it's important to note that the wakizashi was a back up sword, used for close quarters/indoor fighting and beheading defeated opponents.

But getting back to the question (finally), shields were used in ancient Japan but fell out of favour. I think the main reason for this was the predilection of Japanese warriors for two handed weapons, most notably the spear and bow. Both of these are important battlefield weapons, for obvious reasons, and were the preferred weapons of samurai. Samurai were also first and foremost skilled hors*m*n in the Edo period however stirrups were not developed in Japan forcing the samurai to hold reins or grip onto the saddle with their knees whilst using a bow. A shield was impractical for horseback fighting. Fighting on foot was for the low classes of Japan, their force of ashigaru surrounded the samurai on foot.

So basically, two handed spears and bows were hugely popular in Japan and hand held shields aren't particularly useful for archers and spearmen.