A crossbow is a weapon
A weapon, arm, or armament is a tool or instrument used with the aim of causing damage or harm to living beings or artificial structures or systems...

 consisting of a bow
Bow (weapon)
The bow and arrow is a projectile weapon system that predates recorded history and is common to most cultures.-Description:A bow is a flexible arc that shoots aerodynamic projectiles by means of elastic energy. Essentially, the bow is a form of spring powered by a string or cord...

 mounted on a stock that shoots projectiles, often called bolts or quarrel
A quarrel or bolt is the term for the ammunition used in a crossbow. The name "quarrel" is derived from the French carré, "square", referring to the fact that they typically have square heads. Although their length varies, they are typically shorter than traditional arrows.Bolts and arrows have...

s. The medieval crossbow was called by many names, most of which derived from the word ballista
The ballista , plural ballistae, was an ancient missile weapon which launched a large projectile at a distant target....

, a torsion engine resembling a crossbow in appearance.

Historically, crossbows played a significant role in the warfare of East Asia since the 4th century B.C., as well as Europe and the Mediterranean.