The crossbow used a mechanical lock to hold a drawn bow, allowing powerful shots from fortifications, ships, siege works, and infantry lines.
The crossbow is a bow mounted crosswise on a stock, drawn and held by a mechanism so the shooter can aim at leisure and release with a trigger. It was in use across Europe throughout the Middle Ages and dominated missile warfare in most of it.
Its decisive quality is that it separates strength from skill. The power comes from the spanning mechanism rather than the archer's back, so a man trained for days can shoot a weapon that would defeat a lifelong bowman drawing by hand.
That made it the weapon of towns, garrisons and mercenary companies — anyone who needed effective missile troops without a generation to raise them.
The bow, called the prod or lath, is mounted across the front of a wooden stock called the tiller. Early prods are composite — layers of horn, sinew and wood glued together — and from the fourteenth century steel prods become standard.
The string is held by a rotating nut of antler or bone set into the tiller, released by a trigger below. It is a simple and very robust mechanism, and it is what allows the weapon to be spanned, carried loaded and shot at a chosen moment.
Draw weights range enormously, from perhaps 150 pounds on a light hunting weapon to 1,000 pounds and beyond on a heavy steel siege crossbow. Spanning devices scale with them: a belt hook and stirrup for light weapons, then the goat's-foot lever, the cranequin and the windlass for the heaviest.
It came into its own in siege warfare, where a slow rate of shooting matters little and accuracy and penetration matter a great deal. Crossbowmen on walls and in siege lines are a constant of medieval warfare from the eleventh century onward.
In the field crossbowmen usually worked behind a pavise, a large standing shield propped up to cover the shooter while he spanned his weapon — a necessary arrangement, since spanning leaves a man defenceless for several seconds.
The Genoese crossbowmen at the Battle of Crécy in 1346 are the cautionary example. Sent forward exhausted, into rain that had slackened their strings, with their pavises still in the baggage train, they were broken by English archery and then ridden down by their own cavalry — a failure of command rather than of the weapon.
Its strengths are penetration, accuracy and training time. A heavy crossbow delivers more energy than any hand bow, it can be aimed deliberately from a rest, and its user is competent in days rather than years.
It can also be carried loaded, which no bow can. A crossbowman can climb a ladder, wait in ambush or hold a gate with the weapon spanned and ready, and that changes what missile troops can be asked to do.
Its weakness is rate of shooting. One to two bolts a minute against a longbowman's ten to twelve is a fivefold disadvantage in volume, and heavy weapons needing a windlass are slower still. Composite prods also suffer badly in wet weather, as Crécy showed.
It is known in the ancient world and reappears in Europe by the tenth century, spreading rapidly through the eleventh as siege warfare intensified and as towns needed defenders they could equip quickly.
The Second Lateran Council of 1139 condemned its use against Christians, a prohibition often cited as evidence of how feared it was. Its practical effect was negligible: crossbows were used continuously against Christian enemies throughout the following centuries.
Steel prods arrive in the fourteenth century and push draw weights and penetration far higher, and the weapon remains in service well into the sixteenth — outlasting the longbow, and giving way only to the handgun that worked on the same principle of trainability.
Genoese crossbowmen were the most sought-after mercenaries in Europe and served across the continent, to the point that "Genoese" functioned almost as a job description in fourteenth-century accounts.
German and Bohemian workshops led on steel prods and on the cranequin, the geared spanning device that made the heaviest weapons usable in the field, and Central European armouries hold the finest surviving examples.
Italian and Iberian forms tend toward lighter weapons for mounted and skirmishing use, and Mediterranean naval warfare relied heavily on crossbows, where a slow, accurate, penetrating weapon suited fighting from a deck.