"I waste him with my crossbow!"
- – Bob Herzog, Knights Of The Dinner Table
The crossbow is named for its cross-shaped design, as it is basically a bow on a stick that uses a mechanism to trigger the release of either an arrow (called a bolt or quarrel) or a small spherical stone or lead bullet (the latter usually being used for hunting). Bolts are arrows with a shorter shaft, and could range from being lighter than an average arrow to several times heavier. It operates on the same principle as the traditional bow in that a tough bowstring is pulled back to store potential energy in the bow, which upon release of the string, transfers it to a projectile.
While historians are unsure who first made the crossbow, the earliest known crossbows were found in China around 500 BCE. During the Warring States period, crossbows became a preferred ranged weapon of Chinese armies and the use of crossbows certainly aided in the rise of the Qin Dynasty and the beginning of Imperial China. The Greeks and Romans experimented with hand-held crossbows, but they never made extensive use of them, although they did make extensive use of ballista (basically a crossbow scaled up to the size of an artillery piece, and often shot stone instead of scaled up arrows). The Chinese of these times ,on the other hand, had crossbows of all types and shapes: from one-handed repeater crossbows, capable of launching dozens of (fairly weak, but often poisoned) arrows per minute, to absurdly heavy ones, designed to be pulled by legs, rather than arms, and launch arrows the size of small javelin, later with gunpowder-filled bombs on the heading at range, only rivaled by siege engines, though later they passed out in favor of multiple rocket launchers (yes, you read it right). Crossbows began to see widespread use in Europe around 1000 CE, at this time emerged crossbows with steel bow sections, more commonly called arbalasts.
The difference between a bow and a crossbow is that a bow's string needs to be pulled back and held by the user while aiming, while a crossbow has a mechanism that locks the bowstring in a readied state and only requires the user to operate the trigger to release the bolt upon sighting their target. The trigger mechanism evolved over time, as did aids for drawing the crossbow's string. The weight or size of the crossbow certainly had an effect on the mechanisms involved, as light crossbows could be reset by hand, but heavier version could end up using levers or crank-operated windlasses to pull back and cock the string, and tended to use more robust release mechanisms due to the increased stress involved.
In fantasy settings, technologically advanced races who don't (or in limitation) employ firearms as their go-to weapon typically make heavy use of crossbows. It is also the ranged weapon of choice for richer and more experienced mercenaries.
For some reason in a lot of fantasy and medieval fiction it seems to be the preferred ranged weapon of whoever the bad guys are. Examples include A Song Of Ice and Fire (where it seems to be the favorite weapon of King Joffrey), The Lord of the Rings (Uruk-Hai marksmen use crossbows) and different settings of DnD (Drow poisoned repeater crossbows). This may have something to do with crossbows being less relying on the wielder's strengths, stamina and personal skill, and thus regarded as "unfair" weapon compared to bow, it was at one point banned by the pope for use on Christians, although due to it's usefulness on the battlefield this was largely ignored.
The crossbow is also the favored ranged weapon of dwarves in most fantasy fiction, though in this case it may be more than just aesthetics; while it would be fitting for a race known for their technical expertise to use a more complex device, also keep in mind that dwarves would have a harder time using regular bows. A bow's power depends on its draw length, and having shorter arms, dwarves can't get as much power out of a bow. They also need a weapon that can be used more easily in confined spaces, which disqualifies longbows right away. What they do have going for them, though, is great strength, making a crossbow's high draw weight less of an issue for them.
Use in warfare
A major advantage of crossbows over regular bows is that because they're fired using a mechanism instead of depending on human strength to hold the bow in a ready-to-fire position, user fatigue is no longer such a huge factor Additionally, the heavier crossbows could generate more force than most humans thanks to the pulley systems used to cock the string, thus heavier bolts could be thrown, resulting in greater penetration of the target. Possibly its biggest advantage is that it was easier to train the use of a crossbow than bows since the weapon's operation is much less taxing.
Of course, the main drawback with crossbows is that they require a wider range of resources and skills to produce due to the mechanisms involved. Crossbows also generally have a lower rate of fire than bows. At best, a crossbowman can get off about eight shots a minute. More powerful arbalast crossbows that used windlasses could manage about three shots a minute, but could store more energy than a human could physically pull back with bare hands. For these reasons Crossbows excel in a siege situation where the ranges are long and you can duck into cover easily while you're reloading. And since sieges tended to be drawn-out affairs anyway, reload time wasn't as necessary.
That being said, despite crossbows being much more expensive than bows, they were much less demanding on user's skill and physique, meaning you can train as many crossbowmen as you have crossbows and replenish killed ones in just few months of training, while in order to train a bowmen you need to start with kids. So while a single bowman is much more effective than a single crossbowman, you can afford a half-dozen of crossbowmen for the cost of one bowman, and replace lost ones quickly as long as their weapon survives the battle. This is probably why they first took off in Warring States period China, where raising large conscript armies was the name of the game.
It should be noted that despite having much greater draw weights than contemporary bows (above 500 lbs in some cases), crossbows were not proportionally more powerful due to their very short draw length, translating into a much briefer energy transfer. More modern crossbows sometimes address this by using recurve bows, or even by using a bullpup configuration by turning the bow backwards and then pulling the string past the bow. Additionally, the reduced aerodynamic properties of crossbow bolts as compared to arrows mean that they very rapidly lose velocity after a relatively short distance, giving them great punch at short range but reduced effectiveness at longer ranges as compared to bows.
The fact that even relatively poorly trained men armed with crossbows could royally murder fully armored knights, made the crossbow one of the most hated pre-firearm weapons in the Europe, even more than the infamous flamberge. At some point it even came to the pope banning crossbows as unholy weapon not to be used on fellow Christians, but even then they remained popular among mercenaries, rich lords and Protestants. Proud knights could accept deaths from elite long/composite bowmen who like them were training from childhood, but not from some hastily drilled dirty peasant levies whose lord could afford few dozens of crossbows.
Crossbows are still occasionally used for military purposes; while a crossbow's bolts lack the stopping power of modern firearms, the bolts it fires are quieter than any "silenced" firearm and it can also be used for niche purposes such as launching grappling hooks or detonating tripwire-activated mines, and its lower projectile speed means it's much less likely to set off any worn explosives. While its comparatively lower ability to kill outright can be an issue you could use the same solution that the Indian Navy used for this problem and use Cyanide tipped bolts, or take the Rambo route and use bolts with explosive tips.
See Also: Crossbows are Underpowered in d20
Because later crossbows were often too tough to simply pull back unaided, a number of devices were invented to allow the wielder to pull back the string. The device used usually depended upon the weight of the bow, as heavier bows would require more advanced devices that required more time to pull back.
- Stirrup and Belt Hook: Most crossbows you see have a stirrup towards the end for putting your foot through to hold it steady. Combined with a belt worn around the waist with a hook attached to it, the wielder could use their whole body, rather than just their arms, to arm the crossbow.
- Goat's Foot Lever: This was a fairly simple detachable lever that gave the user more leverage when pulling back the string. This could arm the crossbow in a single motion.
- Cranequin: This device used gears and a crank to wind up the bowstring, requiring multiple turns to pull it all the way back.
- Windlass: Like the Cranequin this was a winding device, but it also came with a bulky pulley system that attached to the back of the crossbow. As a result, this was a tremendously powerful pulling system at the expense of needing a lot of time to arm.
- Gloves: Generally leather or some other material, good quality gloves (or some tough callouses) can save one some finger or palm bleeding form trying to pull it by the old fashioned way. Talking from experience, if one is to do it this way, put your entire upper back and arms into it, and pull.
Types of Crossbows
As a general note, crossbows are not ballistas, despite their visual similarity. Unlike Crossbows which store energy in a set of arms which are bent back, Ballistas instead store energy in twisted rope that has a wooden beam pushed into it which is then twisted back farther before firing to store energy. That said, some ballistas are discussed here until a proper "siege" article is consolidated.
- Gastraphetes: an early Greek crossbow, the Gastraphetes, or "belly bow", was cocked by resting the stomach on the and pushing down so that more energy can be stored then an archer could. The Gastraphetes worked slightly different from the classic crossbow, in that its arrow slot was two-piece, with one part attached to the rope. Thus, rather than drawing back the crossbow, you readied it by slamming it into the ground.
- Polybolos: also known as a repeating ballista, the Polybolos is more of a big cross bow since the arms are fixed to the "stock" and don't twist around to fire it. The repeating ballista was fired by turning a wheel connected to a chain back to cock it, the turning it the other way to load it again.
- Chu-ko-nu: Otherwise known as the Chinese repeating crossbow, this is one of the more common types of crossbow seen in fiction. The term "repeating crossbow" brings to mind some bastard combination of Assault rifle and crossbow, which it kinda is and is not. Without doubt, this thing could fire quickly; trained soldiers could loose ten bolts in fifteen seconds. However, because of the mechanism's design, the pumping action that pulled the string back also fired the bolt at the same time, so you could not pull the string back and then aim. Chu-ko-nu's were limited to hip fire giving you almost ork levels of accuracy in exchange for an appreciable volume of fire. Additionally because you were pulling the string back one handed, the bolts had a lot less penetration power than those of a regular crossbow. However, the bolts were often poisoned to make up for that (as seen with the Drow, who make use of the weapon extensively). While no matter how strong the poison on your bolt is, you're not gonna kill a man instantly with a scratch. However, on the battlefield causing enough pain to make a person go into shock is as good as killing them outright, and poison delivers the last one in spades.
- Bed Crossbow: A Chinese peculiarity, where multiple crossbows mounted on a static frame were combined to create an increased draw strength. A precursor to the compound crossbow.
- Bullet Crossbows: These were essentially the same as regular crossbows, except they fired stone or lead shot instead of bolts.
- Crossbow pistol: Small crossbows designed to be fired from one hand, with modernized versions commonly featuring a more modern pistol grip and trigger. While these did exist in the past, they were nowhere near as lethal as battlefield crossbows as the draw weights were far smaller.
- Arbalast: As European armor improved with the development of steel plate crossbows with wooden bow sections were just not cutting the mustard anymore, as such they began making that part out of steel. This meant that the bow could store more energy and launch a projectile farther and faster, significantly improving armor penetration but it also increased the amount of energy required to draw it, often requiring various leavers and cranking mechanisms to reset it.
- Slurbow: A crossbow with a cover over its barrel and a small gap used to draw its string back. Arguably influenced by the pistol, the slurbow was mostly used for firing unfeathered quarrels or darts.
- Sauterelle: The last apparition of a crossbow-like weapon in a modern battlefield for frontline work. In WWI, soldiers had a problem: all the artillery that existed was big and unable to drop explosives accurately into a trench, especially at close range. And on the other hand, thrown hand grenades had the precision but too limited range. As an interim solution the French invented the Sauterelle (grasshopper in French): basically a big crossbow built to lob grenades at around 150 yards distance. Worked decently enough but later in the war they were replaced by small, two-man team infantry mortars that were just as easy to move around and use but had three or four time the range and a better rate of fire.
- Compound Crossbow: the modern version of the crossbow, which is basically a modern compound bow on a rifle stock. Many of these also come equipped with telescopic sights modified with cross-hairs that compensate for the effects of gravity, wind, elevation, and other factors that might affect a bolt's accuracy. They are primarily used for hunting, sport and (unusually) home defense in Britain since everything else has been banned. Also finds military (specifically special forces, not frontline grunts), espionage and law enforcement utility by being used to fire ziplines or grappling hooks, explosive, incendiary, poisoned or gas releasing projectiles, or simply well made darts for a silent kill.
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