The medieval crossbow has been overshadowed by its contemporary rivals for ranged combat. First, the long bow's fame at the hands of the English and Welsh made the crossbow's contributions seem weak. The invention of gun powder and firearms was the second blow to the crossbow's reputation. Nevertheless, the crossbow was a significant advance in military technology of the middle ages.
The medieval crossbow actually has a long history, stretching back to the invention of the gastraphetes or "belly bow." This composite bow was set horizontally across a flat plank of wood. The triggering mechanism held the string while the gastraphetes was loaded with an arrow and allowed even the least skilled defenders to fire arrows with relative accuracy and deadly potential. The gastraphetes was loaded by the person leaning upon it with their belly, hence the name. This "belly bow" design was adapted and improved upon by the Romans and each successive civilisation afterward. In the 14th century, metal bows replaced the more production intensive composite materials to make the crossbow even more deadly and easier to create.
Perhaps the most famous use, or rather lack of use, of the crossbow came during the Hundred Years War between England and France. The English were, by comparison, smaller in number and much less wealthy than their French enemies when the war began in 1337. Fielding large armies of Knights and footmen, the French also hired Italian mercenaries who employed crossbows. The English, on the other hand, had fewer resources and so fielded peasants and yeoman archers with an English version of the Welsh long bow. The bow was extremely difficult to pull and took intensive training to fire effectively. French knights caught up in the throes of Chivalric codes of honour refused to employ the crossbow-wielding Italians and charged the lines of the English only to be mowed down by the armour-piercing arrows of the English.
Despite the early losses and devastation wrought by the long bow, the crossbow did represent a significant leap forward in war technology. Though still premised on the basic principle of the gastraphetes, the medieval crossbow had, by the 14th century, become a very deadly, accurate weapon capable of firing an armour-piercing "bolt" (a shorter, sturdier version of the arrow) up to 200 yards. Better still, the crossbow allowed relatively untrained troops to fire more accurately, reducing the expense of training the troops. German crossbowmen added to their metal-on-oak crossbows, placing spikes or axe heads on the front so that it could be used as a melee weapon should they be attacked by knights or footmen. Finally, because the crossbow required less mobility than either a composite or long bow, crossbow-wielding troops could wear heavier armour, increasing their survival rate.
The invention of gun powder and the advent of firearms began to challenge the crossbow as the ready-to-fire, easy-to-aim weapon of choice. Early guns, however, were cumbersome to load and fire, and so were used to augment other archers. Over the years, however, innovations in gun technology made the crossbow less and less indispensable; the gun's psychological advantage and greater firing rate eventually removed the crossbow from the field of combat by the end of the Renaissance or early enlightenment period.
The ease with which crossbows were made and the minimal training required to use them made medieval crossbows an important part of late Medieval armies. It allowed the fielding of larger armies which could put more arrows into the air on a single volley, reducing the effectiveness of heavy cavalry. Though replaced by guns and overlooked compared to the long bow, medieval crossbows have a surprisingly long life, stretching from ancient Greece to modern hunters and sportsmen.