Artillery Units

Many forces use some type of artillery pieces, at least in sieges. These are usually ballista (or bolt throwers), and catapults of various designs & sizes. The former looks like a massive crossbow, firing massive bolts at the enemy, either directly or indirectly. They hit with enough force to easily pass through a couple of ranks of solders at least. Catapults are used to fire large boulders and other heavy object indirectly at targets obliterating anything that the payload hits.
These weapons are set up at the back lines of a force to stop them being easily targeted. Both require at least two operators (at least one to load it, and one to fire), though they usually use at least three with the final member acting as a spotter for the others. Many armies will have access to two or three such devices, and have the means at least to build catapults. The weapons maintenance, build, and operation requires specific training, so the users end up becoming specialists, known artillerists.
Sometimes the weapons are used to fire specialist payloads. The odd time the ballista are used to fire modified bolts, such as magic infused bolts, bolts coated in toxins or disease causing substances, or coated in flammable material & set alight just before being fired. The catapult is even nastier for this, as the bucket used to hold the ammunition can be treated to stop burning allowing for greater spotting & aiming. It's payload is often larger allowing for greater amounts of dangerous material to be thrown at the enemy. Also, it can be used to fire diseased or decaying corpses of animals, humans & humanoids over defences and into areas that cannot be used for fear of contamination. Certain chemicals can be fired too, causing a similar effect.

Type

Artillery