Petrary is a generic term for a medieval stone-throwing siege engine

Siege engine

A siege engine is a device that is designed to break or circumvent city walls and other fortifications in siege warfare. Some have been operated close to the fortifications, while others have been used to attack from a distance. From antiquity, siege engines were constructed largely of wood and...

 (from the Latin petrus, - stone), used to hurl large rocks against the walls of the besieged city, in an attempt to break down the wall and create an entry point.

Petraries can be either gravity operated, where a large counterweight

Counterweight

A counterweight is an equivalent counterbalancing weight that balances a load.-Uses:A counterweight is often used in traction lifts , cranes and funfair rides...

 drops to propel the missile, or tension operated, where the throwing arm is pulled back against twisted rope or animal sinew, which then provides the power when released.

Catapult

Catapult

A catapult is a device used to throw or hurl a projectile a great distance without the aid of explosive devices—particularly various types of ancient and medieval siege engines. Although the catapult has been used since ancient times, it has proven to be one of the most effective mechanisms during...

, trebuchet

Trebuchet

A trebuchet is a siege engine that was employed in the Middle Ages. It is sometimes called a "counterweight trebuchet" or "counterpoise trebuchet" in order to distinguish it from an earlier weapon that has come to be called the "traction trebuchet", the original version with pulling men instead of...

, mangonel

Mangonel

A mangonel was a type of catapult or siege engine used in the medieval period to throw projectiles at a castle's walls. The exact meaning of the term is debatable, and several possibilities have been suggested. Mangonel may also be indirectly referring to the 'mangon' a French hard stone found in...

 are all types of petrary, but ballista

Ballista

The ballista , plural ballistae, was an ancient missile weapon which launched a large projectile at a distant target....

style armaments, which fired bolts or arrows, would not fit into this category.