Catapults
The term catapult comes from the Greek katapultos, which was the earliest type of ballista. It has developed into ageneric term for a variety of missile throwing engines. There were four basic power sources used for catapults in medieval times: tension, traction, torsion and gravity. The basic tension device is a bow and arrow. It is powered by the tension resulting from bending the bow. This was improved withreinforcements to make the composite bow. A larger version of thecomposite bow, mounted on a frame, was called a gastrafetes, or "belly-bow".