This is how many Western people view the samurai:
Of course, it doesn’t necessarily have to be Tom Cruise, but I’m referring to the mainhand katana and off-hand wakizashi. Indeed, this will make you wonder: why not replace the dagger (wakizashi) with a shield? Certainly, that would be a lot more effective.
In many other samurai depictions, the samurai is wielding a single katana, which seems short enough (unlike the much longer ōdachi) that he could wield a shield at the same time. So, this is a valid question, were it not for the fact that the average samurai looked like this:
Or this:
A Samurai’s primary weapon was the bow (yumi). Archery was considered the prime skill of a warrior, and the well-known Way of the Samurai is more applicable to archery than to swordsmanship (kyūba no michi translates roughly to ‘the way of the horse and bow’).
If you look at a samurai wielding a bow or spear (yari), the question why he isn’t using a shield quickly becomes irrelevant. After all, he has no arm left to carry it with.
The same is true for other two-handed weapons that the samurai used, such as the naginata, ōdachi, and the nagamaki. If you think of samurai as spearmen and archers, rather than swordsman, it becomes more obvious why they didn’t use shields.
There are other contributing factors as well. As I mentioned, samurai essentially followed the ‘way of the horse’. Stirrups weren’t invented yet, so they had to use their knees or hold onto the reins, which made carrying a shield completely impractical.
Additionally, shields in Europe got out of fashion when better armour was developed. Samurai armour was always more than adequate enough to protect against basic arrows (and crossbows weren’t used), so there was no need to use a shield.
And finally, Japan lacked the hellenistic influences that Europe had, where shields were used in formations as a specialised and very effective way of fighting, for example by the Macedonians and Spartans (and later by the Romans). In Japan, ancient warfare developed differently, and there was more focus on individual duels rather than formation fighting, so shields weren’t as popular.
That’s not to say that Japanese samurai never used shields at all, though. Samurai archers would use light wooden shields as cover, usually by placing them in the ground in front of them. Ashigaru matchlocks would use similar shields (tate). You could also argue that ancient samurai, from the Heian period, essentially wore their shields on them. The famous ō-yoroi armour has shoulder plates so large that they are basically shields, although they cannot be used offensively.
So, to summarize this answer:
- Because they needed both their hands for their bow or spear
- Because their armour was strong enough to block most hits and arrows
- Because they lacked the hellenistic influences and history of shield warfare
- Because they couldn’t use a shield effectively on horseback