As a tennis fan, I know that when a right handed player faces a left handed one, there's an element of unfamiliarity that could help the left handed guy win the game.
And that got me thinking about ancient battle, and how a soldier typically holds a sword in his right hand and a shield in his left, and when facing another right handed guy, each sword will be facing a shield.
But what if it was a left handed guy facing a right handed one? Then you'd have both shields on one side, and both swords on the other. Wouldn't that usually throw the right handed guy off because he wouldn't know how to protect himself against an inverted attack? I'm assuming the left handed guy would know what to do because he's training on facing right handed guys all the time.
Is there any historical data or any reports that mention a soldier facing this issue? Was it ever reported as an advantage or a disadvantage during battle? Or did the left handers simply conform and fight right handed to maintain a uniform military?
Thank you
The major concern for a left-handed swordsman is that you would not fit into a tight formation of heavy infantry, such as a Roman maniple or Greek phalanx, which required uniformity and discipline to work. Your shield protected the man to your left as much (if not more) as it protected you. If went into such a formation as a leftie, your shield would double-up with the man to your right, and serve no purpose, while the man to your left would be unprotected. Naturally the enemy would drive for this obvious hole in your shield wall, and the man to your left--indeed all the men in your formation--would quickly grow to hate you and your sinister ways. So if you were a heavy infantry soldier in a military that followed tight formational doctrine, it was pretty much go right or go home.
But for hopeless lefties, there was always work with light infantry, irregulars, archers, skirmishers, cavalry, or specialist roles where strict conformance was not necessary. Lefties who simply could not adapt to the strict handedness of the rank-and-file heavy infantry could always find somewhere else to fit in.
Of course, unit types were often class-based, with family status and wealth determining your placement in the military. If you were from a good family, but not quite good enough to prance around on horses, the general expectation was that you could afford a good suit of armour and shield, and would therefore find yourself situated among the heavy infantry. (It was usually the poor soldiers who could not afford decent body armour, and the really rich ones who could afford horses that were given the jobs of skirmishing.) As a leftie, you might find that your swordsmanship skills were compromised by the strict conformance required of your unit. But it actually wasn't as big a deal as you might think. Unit tactics were not dependent on individual weapon prowess, but on cohesion and discipline. Your left hand was still in operation, after all, using the shield, so the guy to your left might be grateful for your left-handedness, since it improved his own protection. Your own ability to aim and stab with finesse might not be so great, but frankly it wasn't that important a skill in the crush. More important that you stood your ground, supported the soldiers adjacent to you, and moved when they moved. In phalanx-type units, the majority of soldiers would not even be in contact with the enemy, but would be deeper in the ranks providing strength and stability in the othismos, the coordinated push forward. Your handedness hardly mattered in this case.
Now, single combat is an entirely different story. Lefties do tend to have the "southpaw" advantage here, which is simply that they are unusual and less familiar to everyone (including other lefties). It might be a noteworthy thing to cultivate for a gladiator, a tournament fighter, or a duellist. But your question was about soldiers, so I will leave it at that.
Don't really have much to add myself, but there was a previous discussion about castle spiral staircases and the potential for them being designed for defensive purposes relative to a defender's dominant arm:
As an side question would there be any restriction from using your left hand due to its effect on your units formation?