In function, a crossbow is little more than a powerful bow with a trigger. A strong piece of wood, many times less flexible than the kind used for its contemporary the longbow, was fixed perpendicular to the end of another piece. The first piece was strung similarly to a regular bow, but a piece of lightweight cable was fastened to the middle of this string. The other end of this cable was wound around a small winch, attached to the back end of the crossbow. A mechanical trigger was fastened within the body of the crossbow, with a hook above to hold the bowstring before firing.
Crossbows fired a special type of arrow called a bolt, which was placed in a groove in front of a drawn bowstring. The power that the crossbow fired with gave the bolt greatly magnified range and accuracy when compared to an ordinary bow, making it ideal for defending castles or fortresses. However, its versatility was poor due to its unwieldiness, and the rate of fire was very slow due to its reliance on the winch to draw the string.
- The usage of the crossbow by French armies in the Hundred Years' War may have been a factor in their defeat—they proved inefficient against the longbows of England.