This is a ballista, a Roman trebuchet like cannon that derived from early Greek weapons. The earliest form of ballista is thought to date back to 400 BC. This picture is of a ballista that dates nearer to 150 BC. This torsion weapon uses a bow and arrow type of method to function. By pulling back the winches and claw, the bow string (made of animal sinew) gains enough power to shoot the metal shots loaded in the weapon.
This is a carronade, a cannon that was developed around 1770. The carronade pictured here was a 69 pound British Naval cannon. The main purpose of these cannons was to fire short range. These were first considered very successful, but soon diminished as short range encounters were replaced with firing from far away. This cannon had a smaller chamber then bore (a part of the chamber) which decreased the weight, but also reduced the velocity and range it could be fired. This cannon only required a small crew, and therefore was frequently used on merchant ships.
RESOURCES
"Ballista." Wikipedia, the Free Encyclopedia. Web. 02 Feb. 2011. <http://en.wikipedia.org/wiki/Ballista>.
