Ballista

A ballista (plural ballistae) was a large ranged weapon typically used to lay siege to a fortified structure, but it was also used to defend such redoubts. They were also mounted on ships for naval combat.

Description
Ballistae were essentially large, heavy crossbows that were mounted on something sturdy that could withstand the force needed to load and fire the weapon. They could be mounted on heavy carts or wagons, sturdy walls, buildings, or on the decks of ships, for example. Ballistae fired heavy bolts similar to a crossbow but on a large scale.

The rate of fire of a ballista was relatively slow because it took considerable effort to load and aim the weapon. People of medium and smaller stature were at a particular disadvantage. Large creatures could usually operate a ballista with proficiently.