Seruic ballistae are torsion-powered bolt throwers. Built from a combination of wood and metal, they are a common sight on the high walls of Seruic castles.
In simple terms, a ballista is a bow that is mounted on a stand and fires metal bolts instead of arrows. With the help of torsion, ballistae can fire bolts further and with more power than a manual long- or shortbow.
The main structure of a ballista, known as the stand, is constructed from wood and held together with iron plates. On top of the stand is a wooden slider, into which metal bolts are loaded by the ballista operator, and the bow arms, which, for all intents and purposes, is similar to a manual bow. Torsion springs made of animal sinew - often deer - are attached to the bow arms, which are in turn attached to the bowstring. Attached to the slider at the back are a pair of winches and a claw, which are used to ratchet the bowstring back into an armed firing position.
To arm the ballista, the operater loads a bolt into the slider and ratchets the bowstring using the winches. The already-taut torsion springs are stretched further, storing more energy the tighter the bowstring is ratcheted. To fire, the operator releases the catch on the ballista, which releases the stored energy and fires the bolt to devastating effect.
Ballistae were developed in Serukis after the First Dragon War, which took place towards the end of 100 SE (3959 EA). Though the war had been ended by a truce, the Seruic people were nervous of the dragons' aerial superiority and wanted a way to combat that if they ever went to war again.
By 120 SE, the first prototypes of the ballistae had been developed. As the Seruic people were building their castles across the country, they made sure that ballistae were installed on their high walls. Just in case.
When the Second Dragon War began in 663 SE, the ballistae were used to great effect. This time, the Seruic people were no longer out-matched. Along with some dragons betraying their own, ballistae contributed heavily to the Seruic people winning this conflict.