A crossbow is a type of weapon, based on the bow, consisting of a horizontal bow-like assembly mounted on a stock, that shoots projectiles called bolts or quarrels. The medieval crossbow was called by many names, most of which derived from the word ballista, a torsion siege engine resembling a crossbow.
Historically, crossbows played a significant role in the warfare of East Asia, Europe and the Mediterranean. The invention of the crossbow caused a major shift in the role of ranged weaponry among armies, as the traditional bow and arrow had long been a specialized weapons system which required a considerable degree of lifetime training, physical strength and expertise to operate with any degree of efficiency; in many cultures, despite being usually drawn from the common class, bowmen were considered a separate and superior caste, as their archery skill-set (similar to many horseman cultures) was essentially developed from birth and impossible to reproduce outside a pre-established cultural tradition, which many nations lacked.
In contrast, the crossbow was the first projectile weapon to be simple, cheap and physically-undemanding enough to be operated by large numbers of conscript soldiers, thus enabling virtually any nation to field a potent force of ranged crossbowmen with little expense beyond the cost of the weapons themselves. This led to the ascendancy of large mercenary armies of crossbowmen (best exemplified by the Genoese crossbowmen), and the eventual death of the heavily armored aristocratic knight as armies became progressively dominated by conscripts equipped with increasingly-powerful ranged projectile weapons.In modern times, although largely supplanted by firearms in most roles, crossbows are still widely used for shooting sports, hunting, and when shooting in relative silence is an important consideration.