I’m writing a book in a fantasy setting and my main character is a knight. His main weapon is a longsword, with a shortsword as a sidearm. Do you think he should carry a bow as well, or would that not make sense as that is what archers are for?
Normally, a longsword would be the sidearm. The shortsword, or long knife (the terms are analogous) would be a backup weapon. This is more or less how knives are used today. Their primary weapon would probably be a spear, or another polearm of some variety. That said, this is all very dependent on the culture you’re working from, so I’ll loop back to that in a minute.
Mounted archers certainly existed. They would act as skirmishers, harassing enemy infantry at close range, while staying out of melee. It’s a distinct combat role, and not something you’d normally associate with knights. (For reference, mounted archers aren’t the only form of skirmishers. Small squads of archers or even specialized infantry units performed the same role.)
Normally (at least in Europe) the role of the Knight was cavalry. These would be mounted units that charged into enemy infantry to disrupt their formations, then they would either break contact and repeat or they would remain in direct combat against the disrupted infantry.
While charging, cavalry benefits significantly from polearms, (particularly spears and lances.) After the charge, because of the ranges that combat will occur at, a soldier will be better served with a sword. They’ll be stuck in close quarters surrounded by enemy infantry. The horse is a critical part of their armaments, providing a serious advantage, but they’re still attacking people next to their boots. At that point, a sword is a much better tool than a spear.
It’s fairly plausible that your Knight would know how to use a bow, and had received rudimentary training on one, even if they weren’t a master marksman, and didn’t carry one normally. This isn’t so much an endorsement of the idea that they’d need to carry a bow, so much as the basic suggestion that, yeah, these options would be open to your character.
So, that’s reality (specifically historical Europe, where we usually draw the model of a knight from), but, you’re writing a fantasy setting and that may differ significantly from the real world.
When you strip out the specifics of the training, a Knight was an elite, specialized, combatant. Real Knights were trained to do some of the most difficult jobs in Medieval combat, and as a result required substantially more time to prepare. Knights were, in some ways, analogous to modern special forces. This means it’s better for you to tailor your knight’s weapons to the threats they face, rather than suggesting a basic set of gear and asking if that makes sense. It could.
So, if your fantasy setting is “basically Europe,” with the serial numbers filed off, then, yeah, a longsword, shield, spear, dagger, and possibly some kind of ranged weapon like a shortbow, would make sense for your character. Especially if they’re operating on their own or with a small group of other knights errant.
If your setting is swarming with monsters, then a heavier, or more versatile polearm, like a halbard, poleaxe, or voulge may be more useful. Additionally, a heavier bow, and more time spent honing their marksmanship, would be appropriate.
If your setting is densely mountainous, with no real opportunity to use a horse, where most encounters occur in very tight spaces, then you’d probably get more value from the sword than the spear.
A knight’s role in society, their armor, their weapons, even their training, are all part of the larger world that they inhabit. If your fantasy world starts to depart seriously from the real one, you might want to go back and consider what else would change.
For example: if your setting is a volcanic archipelago, with tiny coastal enclaves on the islands, then that world’s knights would need to be equipped for travel by sea, and combat aboard ships. So, lighter armors would be far more useful. Swords (assuming there were sources of iron), would still make sense as a weapon choice, but aboard ship, you wouldn’t have room for polearms. Those might be used during amphibious assaults, however. Your knights would probably still benefit from some kind of ranged weapons, though at that point, thrown options would be better (salt water is not kind to bows, and you never want to get your bow wet.)
So, do your choices sound reasonable? Yeah, they might, if they fit with the world you’re creating.