Crossbow is a weapon from Xth century which perfected bow and arrow. Primitive bow was replaced by a powerful metal arc made of one or several metal canes, called “arbalesta” or crossbow.
Vegetal rope was replace by a wire and later for synthetic fibres in current sports versions. Primitive vegetal cane arrow was replaced by a metal one, able to drill cuirasses, and by a carbon one in the modern ones. A furrowed rail where place the arrow was added to it, for allowing the rope or wire´s movement.
We achieved to bend the metal bow, despite its huge resistance, by some methods:
The first one consisted in putting the bow on the ground and stretching the wire with both hands or foot until holding it back with a hook.
Later, mechanisms were set over the middle rail. The most successful was the stretching through tourniquet or crank. The wire, stretched and held back by a device, was pulled by a trigger.
Its power got incredible levels in its more advanced version, with metal shovels (metal projectile drilled a chainmail at a distance of 350 m. However, oldest and less powerful versions became very used weapons. The main reason was that they were easy to handle, basically they only had to aim and pull the trigger, if compaired to the bow. It meant that an archer trained much more than a crossbowman. For example, the famous welsh bow, used above all by english soldiers during the War of 100 years, was able to drill knight armours or wound with arrows at a distance of 300 m but it needed a 75 kilos stretch. A good archer needed several years of training.
Crossbow could be shooted body to ground, on foot or by horse and it didn´t need so much skill, unlike a bow, to hit the bulls-eye. Its slowness of recharge was its main disadvantage, because while the crossbowman shooted 1bow/min a strong and skilled archer could shot 10 arrows/min.
It existed a repetition throwing system invented in the Ancient China, less powerful, but able to make several shots before reloading. But previously in Middle Age, the ancient greeks seemed to know a primitive version. It was called a “belly bow”, because to stretch it we pushed the mechanism on the belly.
Crossbow was the predecessor of firearms. Because all of them worked aiming a target with the eye and pulling a trigger. The appearance of powder increased its range of reach. Soldiers who carried this kind of weapons were called crossbowmen.