bastard swords and zweihanders are so massive, they have to be carried either at the side of a giant or extremely tall character, of on a person’s back. as well, how well do they work? is it a matter of fighting style, terrain, opponents, all the above? they look so cool and awesome, but are also just so big
So, it’s probably worth saying, up front, the bastard sword is, basically, a modern term. Not, a modern invention per say. The term itself is also not new. But, the way it’s applied today is less than 200 years old.
The bastard sword is just a different name for a longsword. Usually the definition would be, “a longsword with a two handed grip,” but, really, that is most longswords.
So, you’re talking about a sword with a 28″-36″ blade, and a grip you can hold in both hands, or use one handed. Historically, these would have just been called “swords.” Nothing particularly special about them.
As much as I like “zweihander” as a term, it’s probably worth remembering that this is, just, German for “two handed.” They’re long blades, usually around 48″ inches, though they do come longer. They also have a longer grip, to give the user more leverage. These are going to be heavier than a normal sword, but it’ll still be less than your average, domestic house cat.
In general, the etymology of most European two handed swords boils down to, “hey, it’s a big sword.” Even the Claymore is basically just, “hey, it’s a big sword,” in Gaelic. The zweihander is just, “hey, you’re going to need more than one hand to use this,” in German. (Incidentally, there are alternate German names for large swords including bihander. I’ve never come across the German Grossschwert, but it wouldn’t surprise me if that’s an acceptable term as well.)
Beyond that, a zweihander is still a sword, you use it like a sword. This means the normal strike patterns for a blade still work. It’s been scaled up, but not to the point that it’s become unmanageable. The point is to make a sword that can win a game of bleed tag, not turn it into a roving slab you can’t get moving before your opponent has run you through.
Because of the longer grip, two-handed swords do allow for some more fluid, circular strike patterns. From what I know, these were mostly practiced by Spanish and Portuguese schools. If I understand correctly, schools in that region viewed greatswords as a tool for dealing with multiple attackers. I’m not entirely sure if this was simply a drill technique, to get the swordsman used to the idea of moving between opponents, or if they really intended these guys to take on multiple opponents simultaneously. The former seems far more likely, and is a useful skill to cultivate for any combatant.
The major difference between a longsword and a zweihander is reach. A zweihander will let you strike at foes who are not close enough to attack with their blades, while still giving you a way to keep them at range, and punishing them for attempting to close. This is especially true of thrusts with a zweihander, which can vastly exceed what you’d see from a “normal,” longsword.
In most cases two handed swords could be used one handed, but because of the extra weight it was exhausting and the user would sacrifice some fine control over the blade.
You are right about the blade length. At least with the Zweihander. These were long blades, and if you were traveling, you’d probably want to wrap it, and carry across your back or along side your pack. If you were traveling with a horse, you would probably leave that on your horse. If you were expecting trouble, you’d need to get it ready before things got out of hand, because you wouldn’t get the opportunity in the moment. Also, unlike large axes, polearms, or staves, you couldn’t really use on as a walking aid when not in use. And, yes, just because you can’t draw a sword from your back doesn’t mean you can’t keep one there for later.