When building catapults, armies had to include in their ranks those people capable of employing complicated mathematical formulas and turning them into machines of war.
While their appearance on warfare scene dramatically changed tactics for quite literally hundreds of years, it was no easy task for medieval armies to create machines of war they needed to help ensure victory.
The engineers were generally responsible for production or mass production of larger scale weapons on battlefield and leading up battle.
When building catapults on site, engineers had to rely on their own know how and materials available to them, unless of course they transported wood, sinew and in case of some more complex catapults, counterpoises and other materials with them.
When idea was to create more simple machines such as ballistas or mangonels, task of building catapults was much easier on site than let’s say a trebuchet, which often required extremely heavy materials. In case of ballistas and mangonels, main ingredients – wood and rope or sinew – were a little easier for engineers to find. The difficulty came in getting these machines together in a big hurry for an impending siege.
Since mass production factories and automation were years in future, medieval armies had to rely on their own ingenuity to pull this off. Engineers who were responsible for building catapults understood intricacies of design, they knew formulas behind trajectory theory and they were smart enough to create ways to make their designs more mobile and easier to construct with haste.
When building catapults such as ballista and mangonel, engineers only needed to create simple designs. The ballista, for example, required a platform, two wooden arms and tightly wound ropes. These machines could be built in advance and put on platforms for an army to move along with it. The mangonel, too, was similar, and building catapults of this make required only one wooden arm. The drawback to both of these machines, however, was lack of accuracy, although mobility was a plus.