How Crossbows Work

Crossbow Advantages

Crossbows don't require the same physical strength or training that ordinary bows do:

When using a traditional bow, an archer must draw, aim and shoot in fairly quick succession. The longer it takes the archer to aim, the more fatigued his arm will become, and the less accurate his shot will be. Being able to aim and shoot quickly requires lots of practice. But if the archer uses a crossbow, he can draw the string -- or cock the crossbow -- and leave it that way as long as he needs to.
An archer who isn't very tall can't use a very long bow. If he isn't very strong, he also can't draw the string on a powerful bow. In other words, a person's size and upper body strength limit the size and strength of the bow he can use. With a crossbow, though, an archer can use his strongest muscle groups -- the ones found in his thighs and buttocks -- to draw the string. A crossbowman can even use tools like levers or cranks to supplement his strength. This means that a crossbowman can use a more powerful weapon than a traditional archer with the same amount of strength.

Early crossbows did have a few disadvantages, though. An archer could load, aim and shoot a bow in around six seconds, but a crossbowman required nearly a minute to do the same task. Crossbows also had far more moving parts than plain longbows. But crossbows gave armies the option of arming recruits with ranged weapons regardless of their level of skill at archery.

In general, military crossbows could be very fast or very powerful, but not both. For example, in the 14th century, European crossbow makers began making weapons from steel and incorporating crannequins in their design. A crannequin was a toothed wheel attached to a crank. When a soldier turned the crank, the wheel moved a toothed rod, which pulled the bowstring and cocked the crossbow. With a crannequin, a soldier could cock crossbows that he would not have the strength to cock on his own. However, the soldier had to remove the crannequin before each shot, and re-cocking and reloading a crossbow with a crannequin could take several minutes.

At the other end of the spectrum, some Chinese crossbows were built for speed. Designers added cocking levers and magazines full of bolts to the basic crossbow. Bolts would automatically fall from the magazine when the string was cocked. Often, the crossbow then automatically released the bolt. With this type of crossbow, a soldier could fire several shots per second, although the bolts did not travel as fast or do as much damage as a bolt shot from a steel crossbow with a crannequin.

But regardless of whether it's built for strength or speed, a crossbow's basic function is basically the same as a bow's. We'll look at the factors that affect a bow's power and speed in the next section.