The crossbows seem to appear during the first crusade. It is so deadly a weapon that the church will forbid its use for fighting among Christians ! It works slowly, two shots per minute where a bowman can draw 12 arrows, but training a crossbowman is a matter of days, where a bowman needs several years. The crossbow will prevail at the end of the middle age, due to the irreversible entry of the city militia in the warfare.
The bow of this replica is bent using a winch.
Beware, even if the mechanism works, it is not made for firing : breaking pieces is possible, resulting in potential lethal damages to the user.