Within the world of medieval warfare, there were multiple kinds of siege weapons:  ballistas, battering rams, trebuchets, and catapults.  ‘Catapult’ can be used as a more general term for all throwing siege weapons:  “Catapults are siege engines using an arm to hurl a projectile a great distance. Any machine that hurls an object can be considered a catapult, but the term is generally understood to mean medieval siege weapons.

The name is derived from the Greek ‘to hurl a missle’.  Originally, “catapult” referred to a stone-thrower, while “ballista” referred to a dart-thrower, but the two terms swapped meaning sometime in the fourth century AD.

Catapults were usually assembled at the site of a siege, and an army carried few or no pieces of it with them because wood was easily available on site. Catapults can be classified according to the physical concept used to store and release the energy required to propel the projectile.”  http://www.claymoreslinger.com/medieval_catapult.asp

My son has built a trebuchet for his senior project.   He’s the tall one in the picture, with assorted brothers and cousins.

Ballista:  “One of the siege weapons used during the Middle Ages include the Ballista. The Ballista was an invaluable Medieval siege attack weapon. The Ballista design was similar to a giant crossbow and worked by using tension. The Ballista was designed to aim huge wooden, iron clad, darts or arrows which were powered by twisted skeins of rope, hair, or sinew – the ballista design was based on a huge dart-throwing machine. The Ballista loosed heavy bolts, darts and spears along a flat trajectory. The force of the missiles launched from the Ballista was designed to have great penetration and were capable of skewering several of the enemy at one time!”  http://www.middle-ages.org.uk/ballista.htm

Battering Ram:  “The concept behind the battering ram is simple – momentum coupled with mass. In other words, take a heavy object and hurl it repeatedly at a stationary object, such as a door or gate, to break through the object. Typically a large tree would be felled and the branches removed to allow those that remained to be used as grips. A group of soldiers would lift the tree trunk and, after a running start to build momentum, ram the trunk into whatever they wanted to break through, generally a castle gate. If this was done enough times, the door would break open.

Sometimes the tree trunk was affixed to a support system that was then positioned in front of the door or gate and swung like a pendulum. This allowed larger rams to be used, operated by fewer men. The support system could also be covered to shield and protect those operating the ram from attack.”  http://www.medieval-period.com/medievalbatteringram.html

Trebuchet:  “Trebuchets were used to throw stones–or dead animals–with great accuracy. A trebuchet was capable of launching 200lb. projectiles towards virtually anything. We can define a trebuchet as “the atom bomb of its time.” Earlier trebuchets could only fire small stones or even cows. As time passed and as trebuchets were improved (Leonardo Da Vinci dramatically improved them) they were able to launch huge projectiles towards a castle’s walls.

Many persons were needed to operate a trebuchet. Trial-and-error was the method used to destroy a wall. When a certain point of a castle was targeted, the trebuchet was so accurate that it could remain firing almost invariantly at that same spot; making them very effective.

With trebuchets, invading armies could fire cows and other dead animals from a relatively large distance. The only downside of trebuchets was their enormous size. In earlier medieval times, it was very hard to transport such gigantic machinery. As they were improved, new methods to arm them were discovered.”  http://www.medieval-castles.org/index.php/medieval_trebuchet  The picture shows Carew firing a water balloon.  The video below shows the trial and error involved in getting it right.  As it turned out, it wasn’t launching the water balloons far at first because the rope on the sling was too long and the angle of the ‘finger’ at the end (onto which the rope was hooked) was angled too sharply.