Answer:
The role of catapults was to throw stones and flammable oil, to weaken the security that could be forming behind the city walls.
Step-by-step explanation:
Mongols were very violent warriors and in each of their conquests they seized equipment and objects that could help them win the battles they would have in the future. They seized the catapults when they invaded Chinese territory and quickly learned to handle them, which was an extremely positive factor in their battles.
That's because catapults allowed Mongolians to make successful sieges. Outside the cities, they hurled stones and flammable oil, to cause destruction within the cities and to diminish possible defenses, which made the invasion much easier.